Structured-text cataloging method, structured-text searching method, and portable medium used in the methods

ABSTRACT

A text cataloging method includes a step of cataloging already-analyzed-text data obtained from an analysis of a logical structure of a text to be cataloged in a text database, a step of creating a structure index by sequentially superposing logical structures of texts to be cataloged, wherein a single metaelement is used for representing a group of elements in the texts having the same position of appearance in one of the texts and the same element type, a single piece of meta-character-string data is used for representing a group of pieces of character-string data in the texts having the same position of appearance in one of the texts, and a context identifier is assigned to each metanode composing a tree-like structure of the structure index for uniquely identifying the metanode; a step of generating structured-full-text data composed of definitions of associative relations between all pieces of character-string data included in already-analyzed-text data of each text to be cataloged, and context identifiers of pieces of meta-character-string data in the structure index used for representing the pieces of character-string data; and a character-string-index updating step, including the sub-steps of extracting partial character strings, generating structured-character-position information, and updating a character-string index.

The above-referenced patent application is a continuation of U.S. Ser.No. 09/814,692, filed Mar. 15, 2001, now U.S. Pat. No. 6,389,413 whichis a continuation application of U.S. application Ser. No. 09/589,226,filed on Jun. 8, 2000 (now U.S. Pat. No. 6,226,632), which is acontinuation application of U.S. Ser. No. 09/028,513, filed Feb. 23,1998 (now U.S. Pat. No. 6,105,022), from which priority is claimed under35 U.S.C. §120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to text cataloging and textsearching in a text control system utilizing a computer. Moreparticularly, the present invention relates to a method for cataloging astructured text in a set of structured texts, each of which has alogical structure, and a method for searching such a set of structuredtexts for specific text content at a high speed. The invention alsorelates to a portable medium used in the text cataloging and textsearching methods.

2. Description of the Related Art

With the development of the information society making full-scaleprogress, the amount of electronically-prepared text-based informationcreated by using an apparatus such as a word processor and a personalcomputer is increasing at an extraordinarily high pace. Under thiscircumstance, the demand to search a massive collection of cumulatedelectronically-prepared texts for desired information with a high degreeof reliability is rising.

In response to the demand, technology for full-text searching has beendeveloped in which full texts are cataloged in a computer system andtreated as a database. Since the database is then searched for aspecified string of characters (which is referred to hereafter as a“search term”), a keyword is not required, basically allowing a searchoperation to be carried out with no detection miss.

A text comprising logical structure elements that can be individuallyrecognized can be treated as an object to be searched in a searchoperation. Such a text is referred to hereafter as a “structured text”.An example of a structured text is a text described in SGML (StandardGeneralized Markup Language (ISO 8879:1986)). In such a searchoperation, a condition regarding a logical structure is added to a listof search conditions, allowing a search operation with highly detailedsearch conditions to be carried out.

An example of a search system implementing a search operation specifyinga structure condition is disclosed in Japanese Patent Laid-Open No. Hei8-147311 (JP '311). In this structured-text searching method, when atext is cataloged, the original of the text is cataloged in a searchdatabase. Then, specific character strings representing the head and theend of each logical structure of the cataloged text original aredetected to identify logical structures. At the same time, the text isdivided into logical structures. The specific character stringsrepresenting the head and the end of each logical structure are referredto hereafter as a “front marker” and a “back marker”, respectively.

In the case of an electronically prepared specification for a patentapplication, for example, the front and back markers detected asdelimiters of the range of a logical structure called “Abstract of theDisclosure” are “<SDO ABJ>” and “</SDO>” respectively. The front andback markers are detected to cut out a text delimited thereby as a textof the logical structure. Other logical structures are cut out in thesame way in order to divide the original text into logical structures.

Next, a condensed-text creating process is carried out on the originaltext of each of the resulting logical structures. In the case of thelogical structure “Abstract of the Disclosure”, for example, theoriginal text is divided into phrase character strings, each of whichcomprises word units, and a mutual-inclusion relation among the phrasecharacter strings is examined. Then, by eliminating a string ofcharacters included in another phrase character string, a condensed textof the logical structure can be produced. By carrying out the samecondensed-text creating process on other logical structures, a condensedtext can be formed for each of the other logical structures. Thecondensed texts are then cataloged in a search database as acondensed-text file.

Then, the binary value “1” is set in a bit associated with the code ofeach character appearing in the text in order to create a charactercomponent table, which is also cataloged in the search database as acharacter component table file.

After the search database has been constructed in this way, text searchprocessing is carried out as follows.

First, a specified search term is disassembled into character units. Atext including all characters composing the search term is thenextracted by referencing the character component table.

Then, a condensed-text file to be searched, which contains a logicalstructure specified as a search object, is selected among condensed-textfiles containing logical structures. By searching the charactercomponent table therein, only a condensed text of a text extracted bythe operation to search the character component table can be selected asa search object. As a result, a text including the specified search termincluded in a specified logical structure can be extracted. If nopositional relation in the text among a plurality of search terms isprescribed in a specified search condition equation, the searchprocessing is ended. If such a positional relation is specified, on theother hand, the contents of sentences included in a text extracted as aresult of the search of the condensed text are read. Only if all thespecified search terms are found in the extracted text and, at the sametime, the positional relation among the search terms satisfies thespecified search condition equation, is the extracted text confirmed asthe desired text.

As described above, the search method according to JP '311 allows apractical speed for a search operation to be maintained for alarge-scale database and, at the same time, allows a search operationspecifying a structure condition to be carried out.

According to the technology described in JP '311, a search operationspecifying a certain structure condition can be carried out. With thisstructure specifying technique, however, a search operation satisfying asubtly specified structure condition cannot be carried out in somecases.

In the text cataloging/searching system provided by JP '311, thestructure of a text to be cataloged is divided into sub-structuresdetermined in advance, and a condensed-text file is created for eachsub-structure. In a search operation, a file defining a relationassociating the names of sub-structures and the names of condensed-textfiles is referenced to determine a set of condensed-text files to besearched. A search operation specifying a structure condition is thenimplemented by carrying out the search operation with onlycondensed-text files in the set treated as a search object.

In text cataloging/searching this system, at a stage of constructing atext database, the designer of the database predicts the structureconditions that are thought to be specified in search operations to becarried out in the future. Then, a text is divided into condensed-textfiles that allow search operations to be carried out in conformity withthe predicted structure conditions. In consequence, however, a searchoperation that satisfies a structure condition which was not predictedwhen the database was constructed cannot be carried out.

For example, assume that a text is divided into two logical elementswhich are each referred to hereafter simply as “elements”. Let the twoelements be called “abstract” and “main body”, respectively. Consideringthat the “main body ” element is further divided into any arbitrarynumber of paragraphs which are each composed of the title of theparagraph and any arbitrary number of sections, if two condensed-textfiles for the “abstract” and “main body” elements are created andcataloged in a text database containing a set of texts organized intosuch a structure in a process of constructing the database, a searchoperation satisfying a structure condition stating: “Find a group ofsentences in the title of a paragraph that includes a string ofcharacters OO” cannot be carried out.

Instead of treating the “main body” element as a single condensed-textfile, the title of each paragraph and the sections composing the elementcan each be treated as a condensed-text file, allowing a searchoperation satisfying the structure condition described above to becarried out. Even if such condensed files are provided, however, asearch operation will not be able to keep up with structure conditionssuch as ones stating: “Find a group of sentences including a string ofcharacters OO inside the first paragraph (which can be either the titleof the first paragraph or a section in the first paragraph),” or “Find agroup of sentences including a string of characters XX in the lastsection of a paragraph.” In order to keep up with a structure conditionincluding such a specification of a specific position of a search term,a condensed-text file needs to be provided separately in advance for theappearance of each paragraph and each section. In this case, not onlydoes the number of condensed-text files provided for paragraphs andsections become extremely large because such paragraphs and sections canappear in an element in any arbitrary manner, but a search operationsatisfying such a condition cannot be actually carried out because themethod described in JP '311 is not provided with a means for associatinga structure condition that includes any arbitrary specification of aposition of appearance of a search term with a set of smallcondensed-text files resulting from finely disassembling each element.

It is thus impossible to include an order of appearance condition in thespecification of a structure condition as described above, so that asearch operation with a very detailed structure specification cannot becarried out.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to solve the problemsdescribed above by providing a function for carrying out a searchoperation specifying a detailed and efficient structure.

In order to solve the problems described above, the present inventionprovides a text cataloging method that comprises:

(1) an already-analyzed-text data generating/cataloging step ofcataloging already-analyzed-text data, which is obtained from ananalysis of a logical structure of a text to be cataloged, in a textdatabase;

(2) a structure-index creating step of creating a structure index bysequentially superposing logical structures of texts to be cataloged,one upon another, in the structure index in the same order as thechronological order in which the texts are cataloged, wherein a singlemetaelement is used for representing a group of elements in the textshaving the same position of appearance in one of the texts and the sameelement type, a single piece of meta-character-string data is used forrepresenting a group of pieces of character-string data in the textshaving the same position of appearance in one of the texts, and acontext identifier is assigned to each metanode composing a tree-likestructure of the structure index for uniquely identifying the metanode,where “metanode” is a generic name for a metaelement andmeta-character-string data;

(3) a structured-full-text-data generating step of generatingstructured-full-text data composed of definitions of associativerelations between all pieces of character-string data included inalready-analyzed-text data of each text to be cataloged, and contextidentifiers of pieces of meta-character-string data in the structureindex used for representing the pieces of character-string data;

(4) a character-string-index updating step comprising the sub-steps of:

extracting partial character strings each having a predeterminedcharacter count, character-position information of the partial characterstrings in a text to be cataloged, a text identifier for uniquelyidentifying the text in a text database, and a context identifier ofmeta-character-string data representing character-string data includingthe partial character strings in a structure index from thecharacter-string data included in each text to be cataloged;

generating structured-character-position information comprising thecharacter-position information, the text identifier and the contextidentifier; and

updating a character-string index by cataloging an associative relationbetween each of the partial character strings and thestructured-character-position information in the character-string index.

In addition, the structured-text searching method provided by thepresent invention comprises:

(1) a structure-condition judging step of searching a structure indexfor a set of context identifiers satisfying a specified structurecondition;

(2) a structured-character-position-information extracting step ofextracting partial character strings, each of which has a predeterminedcharacter count, from a search term, and searching a character-stringindex for a set of pieces of structured-character-position informationmatching the partial character strings; and

(3) an index searching step of searching the set of pieces ofstructured-character-position information for specific pieces ofstructured-character-position information that have context identifiersincluded in the set of context identifiers found at thestructure-condition judging step, and that have a positional relationamong the specific pieces of structured-character-position informationmatching the arrangement order of the partial character strings in thesearch term.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overall configuration of a firstembodiment implementing a text searching system provided by the presentinvention;

FIG. 2 is a diagram showing the configuration of a text catalogingsub-system implemented by the first embodiment of the present invention;

FIG. 3 is a PAD showing a procedure for cataloging a text adopted by thefirst embodiment of the present invention;

FIG. 4 is a diagram showing an example of the DTD defining a logicalstructure of a text;

FIG. 5 is a diagram showing an example of a text written in SGML inaccordance with the DTD shown in FIG. 4;

FIG. 6 is a model diagram showing diagrammatically the logical structureof the text written in SGML shown in FIG. 5;

FIG. 7 is a PAD (Problem Analysis Diagram) showing details of theprocedure carried out by a text-structure analyzing program provided bythe first embodiment of the present invention;

FIG. 8 is a diagram showing the data structure of a text-structuretable;

FIG. 9 is a PAD showing details of the procedure carried out by astructure-index creating program provided by the first embodiment of thepresent invention;

FIG. 10 is a diagram showing an order of tracing already-analyzed-textdata in the first embodiment of the present invention;

FIG. 11 is a diagram showing an associative relation between a group ofnodes composing the tree-like structure of already-analyzed-text datashown on the left-hand side of the figure and a group of nodes (strictlyspeaking, metanodes) composing the tree-like structure of a structureindex for the already-analyzed-text data shown on the right-hand side ofthe figure, in the first embodiment of the present invention;

FIG. 12 is a diagram showing a process for developing a structure indexby sequentially superposing a plurality of pieces ofalready-analyzed-text data one after another, in the first embodiment ofthe present invention;

FIG. 13 is a PAD showing details of a procedure carried out by astructured-full-text-data generating program in the first embodiment ofthe present invention;

FIG. 14 is a diagram showing a format in which structured-full-text datais output by the structured-full-text-data generating program to a filein the first embodiment of the present invention;

FIG. 15 is a PAD showing details of the procedure carried out by acharacter-string-index creating program in the first embodiment of thepresent invention;

FIG. 16 is a diagram showing the data structure of a character-stringindex used in the first embodiment of the present invention;

FIG. 17 is a diagram showing the configuration of a text searchingserver implemented by the first embodiment of the present invention;

FIG. 18 is a PAD showing a procedure for searching a text adopted by thefirst embodiment of the present invention;

FIG. 19 is a PAD showing details of the procedure carried out by asearch-condition analyzing program in the first embodiment of thepresent invention;

FIG. 20 is a diagram showing an example of generation ofalready-developed-search-condition data in processing carried out by thesearch-condition analyzing program in the first embodiment of thepresent invention;

FIG. 21 is a PAD showing details of the procedure carried out by acharacter-string-index searching program in the first embodiment of thepresent invention;

FIG. 22 is a diagram showing a concatenation judging process carried outby the character-string-index searching program in the first embodimentof the present invention;

FIG. 23 is a diagram showing the structure of search-result data in thefirst embodiment of the present invention;

FIG. 24 is a PAD showing a detailed procedure of the processing totransfer already-analyzed-text data in the first embodiment of thepresent invention;

FIG. 25 is a diagram showing the configuration of a text searchingclient in the first embodiment of the present invention;

FIG. 26 is a PAD showing an operational procedure carried out by thetext searching client provided by the first embodiment of the presentinvention;

FIG. 27 is a PAD showing a detailed procedure of processing carried outby the search-condition inputting program in the first embodiment of thepresent invention;

FIG. 28 is a PAD showing a detailed procedure of processing carried outby the search-result displaying program in the first embodiment of thepresent invention;

FIG. 29 is a diagram showing the configuration of a text catalogingsub-system as implemented by a second embodiment of the presentinvention;

FIG. 30 is a PAD showing a procedure for cataloging a text adopted bythe second embodiment of the present invention;

FIG. 31 is a PAD showing details of the procedure carried out by areversed-order-structure-index creating program in the second embodimentof the present invention;

FIG. 32 is a diagram showing an order of tracing already-analyzed-textdata in the second embodiment of the present invention;

FIG. 33 is a diagram showing an associative relation between a group ofnodes composing the tree-like structure of already-analyzed-text datashown on the left-hand side of the figure and a group of nodes (strictlyspeaking, metanodes) composing the tree-like structure of areversed-order-structure index for the already-analyzed-text data shownon the right-hand side of the figure in the second embodiment of thepresent invention;

FIG. 34 is a diagram showing a process to develop areversed-order-structure index by sequentially superposing a pluralityof pieces of already-analyzed-text data one after another in the secondembodiment of the present invention;

FIG. 35 is a PAD showing details of the procedure carried out by astructured-full-text-data generating program in the second embodiment ofthe present invention;

FIG. 36 is a diagram showing the format in which structured-full-textdata is output by the structured-full-text-data generating program to afile in the second embodiment of the present invention;

FIG. 37 is a diagram showing the data structure of a character-stringindex used in the second embodiment of the present invention;

FIG. 38 is a diagram showing the configuration of the text searchingserver implemented by the second embodiment of the present invention;

FIG. 39 is a PAD showing a procedure for searching a text adopted by thesecond embodiment of the present invention;

FIG. 40 is a PAD showing details of the procedure carried out by asearch-condition analyzing program in the second embodiment of thepresent invention;

FIG. 41 is a diagram showing an example of generation ofalready-developed-search-condition data in processing carried out by thesearch-condition analyzing program in the second embodiment of thepresent invention;

FIG. 42 is a PAD showing details of the procedure carried out by acharacter-string-index searching program in the second embodiment of thepresent invention;

FIG. 43 is a diagram showing an associative relation between a group ofnodes composing the tree-like structure of already-analyzed-text datashown on the left-hand side of the figure and a group of nodes (strictlyspeaking, metanodes) composing the tree-like structure of a structureindex for the already-analyzed-text data shown on the right-hand side ofthe figure in a third embodiment of the present invention;

FIG. 44 is a diagram showing the configuration of a text catalogingsub-system as implemented by the third embodiment of the presentinvention;

FIG. 45 is a PAD showing a procedure for cataloging a text adopted by afourth embodiment of the present invention;

FIG. 46 is a PAD showing the procedure of processing carried out by atext-structure normalizing program in the fourth embodiment of thepresent invention; and

FIG. 47 is a diagram showing an example of the normalization processingin the fourth embodiment of the present invention.

DESCRIPTION OF TEE PREFERRED EMBODIMENTS

The present invention will become more apparent from a careful study ofthe following detailed description of some preferred embodiments withreference to accompanying diagrams.

First Embodiment

FIG. 1 is a diagram showing an overall configuration of a firstembodiment implementing a text searching system provided by the presentinvention. As shown in this figure, the first embodiment comprises atext cataloging sub-system 101, a text searching server 102, textsearching clients 103 and 104, and a network 105.

The text cataloging sub-system 101 analyzes the structure of each textsupplied thereto as a search object and creates index data required in asearch operation. The index data is transmitted to the text searchingserver 102 by way of the network 105 to be used by the text searchingserver 102 in structured-text search processing.

The text searching server 102 receives a search command from the textsearching client 103 or 104, and searches a database for text contentsmatching a search condition specified in the command by using the indexdata created by the text cataloging sub-system 101. The data resultingfrom the search operation is transmitted to the text searching client103 or 104 issuing the search command as a response to the command.

The text searching client 103 or 104 has a display screen on a displayunit. The screen is used by the user for specifying a search conditionin an interactive manner. The search condition specified by the user onthe screen is converted into a search command that can be interpreted bythe text searching server 102.

The search command is transmitted to the text searching server 102 byway of the network 105. Receiving the search command, the text searchingserver 102 carries out search processing in accordance with the searchcommand as described earlier, and transmits the data resulting from thesearch operation to the text searching client 103 or 104 that issued thesearch command, as a response to the command. The text searching client103 or 104 displays the data resulting from the search operation on ascreen to the user.

As shown in FIG. 1, the present embodiment includes two computersserving as the text searching clients 103 and 104 respectively. Itshould be noted, however, that the configuration can also employ onlyone or more than two computers, each serving as a text searching client.

The network 105, which can be implemented by a local area network or awide area network, is used for exchanging various kinds of data andcommands among the text cataloging subsystem 101, the text searchingserver 102, and the text searching clients 103 and 104.

In the text cataloging and searching system shown in FIG. 1, index datais transmitted from the text cataloging sub-system 101 to the textsearching server 102 by way of the network 105 as described above. It isalso possible to have a configuration wherein a portable medium such asa floppy disk, an optical magnetic disk, or a writable optical disk isused for transferring index data from the text cataloging sub-system 101to the text searching server 102 in place of the network 105. As analternative, it is also possible to build a configuration wherein thetext cataloging sub-system 101 and the text searching server 102 areimplemented by a single computer so that no data transfers are neededbetween the text cataloging sub-system 101 and the text searching server102.

In addition, in the configuration shown in this figure, the textsearching clients 103 and 104 and the text searching server 102 areimplemented by three separate computers. However, one or more textsearching clients and the text searching server may be implemented by asingle computer.

FIG. 2 shows the configuration of the text cataloging sub-system 101implemented by the present embodiment.

As shown in this figure, the text cataloging sub-system 101 comprises adisplay unit 201, a keyboard 202, a central processing unit (CPU) 203, afloppy-disk drive 204, a floppy disk 205, a communication controlapparatus 206, a main memory unit 207, a magnetic-disk drive 208, and asystem bus 209.

The display unit 201 is used for displaying information such as anoperating state of the text searching server 102, and the keyboard 202is used for entering a command for requesting an operation, such asexecution of processing to catalog a text. The central processing unit203 executes a variety of programs constituting the functions of thetext cataloging sub-system 101. The floppy-disk drive 204 is used forreading out and writing data from and into the floppy disk 205. Thefloppy disk 205 is used for storing a text to be cataloged in advanceand for providing the text to the text cataloging sub-system 101.

The communication control unit 206 is used for communicating with thetext searching server 102 through the network 105 in order to send arequest to and receive data from the text searching server 102. The mainmemory unit 207 is used for storing a variety of programs to be executedfor carrying out various processes of the text cataloging sub-system101, and for holding data temporarily. The magnetic-disk drive 208 isused for storing cataloged text data and index data generated by thetext cataloging sub-system. The system bus 209 is used for connectingthe display unit 201, the keyboard 102, the central processing unit 203,the floppy-disk drive 204, the floppy disk 205, the communicationcontrol apparatus 206, the main memory unit 207, and the magnetic-diskdrive 208 to each other.

Including also a work area 216, the main memory unit 207 is used forstoring a text-structure analyzing program 210, a structure-indexcreating program 211, a structured-full-text-data generating program212, a character-string-index creating program 213, a text-catalogingcontrol program 214, and a system program 215. In the magnetic-diskdrive 208, an already-analyzed-text-data storing area 217, astructure-index storing area 218, a structured-full-text-data storingarea 219, and a character-string-index storing area 220 are preserved.

The text-structure analyzing program 210 retrieves a text to becataloged, which is written in SGML, from the floppy disk 205, analyzesthe logical structure of the text, generates already-analyzed-text data,and stores the already-analyzed-text data in thealready-analyzed-text-data storing area 217. The structure-indexcreating program 211 catalogs information on a logical structureincluded in the already-analyzed-text data into a structure index storedin the structure-index storing area 218, updating the structure index.

The structured-full-text-data generating program 212 generatesstructured-full-text data for the text to be cataloged from thealready-analyzed-text data, storing the structured-full-text data intothe structured-full-text-data storing area 219. Thecharacter-string-index creating program 213 generates data representingan associative relation between each partial string of characters havinga predetermined length and structured-character-position information forthe partial string of characters from the structured-full-text data, andcatalogs the data in a character-string index stored in thecharacter-string-index storing area 220, updating the character-stringindex.

The text-cataloging control program 214 controls the activation and theexecution of the text-structure analyzing program 210, thestructure-index creating program 211, the structured-full-text-datagenerating program 212, and the character-string-index creating program213. The text-cataloging control program 214 also transmits thealready-analyzed-text data generated by the text-structure analyzingprogram 210, the structure index generated by the structure-indexcreating program 211, and the character-string index generated by thecharacter-string-index creating program 213 to the text searching server102 by way of the network 105. The system program 215 provides basicfunctions for executing the programs implementing the functions of thetext cataloging sub-system 101 on the computer. These basic functionsinclude functions for inputting and outputting data from and toperipheral devices. The work area 216 is used for storing data requiredtemporarily in the execution of the programs.

As described above, the present embodiment has a configuration wherein atext to be cataloged is input from the floppy disk 205. However, it isalso possible to build a configuration wherein another kind of portablemedium, such as an optical magnetic disk or a writable optical disk, isused in place of the floppy disk 205. As an alternative configuration, atext to be cataloged can also be input through the network 105.

In addition, in the configuration of the present embodiment, thealready-analyzed-text data generated by the text-structure analyzingprogram 210, the structure index generated by the structure-indexcreating program 211, and the character-string index generated by thecharacter-string-index creating program 213 are transmitted to the textsearching server 102 by way of the network 105. Instead of using thenetwork 105, however, the present invention is also applicable to aconfiguration wherein a portable medium such as a floppy disk, anoptical magnetic disk, or a writable optical disk can be used fortransferring the information. As an alternative, it is also possible tobuild a configuration wherein the text cataloging sub-system 101 and thetext searching server 102 are implemented by a single computer so thatno data transfers are needed between the text cataloging sub-system 101and the text searching server 102.

Next, a procedure for cataloging a text adopted in the presentembodiment is explained.

FIG. 3 is a PAD (Problem Analysis Diagram) showing a procedure forcataloging a text according to the first embodiment of the presentinvention. When the text-cataloging control program 214 is invoked by acataloging requesting command entered via the keyboard 202, for example,the program examines whether texts to be cataloged exist in the floppydisk 205. If such texts exist, the program determines the number of suchtexts. At Step 301, a series of pieces of processing are carried out forall texts to be cataloged at Steps 302 to 307.

At Step 302, an unprocessed text to be cataloged is selected andretrieved from the floppy disk 205. At Step 303, a text identifier isassigned to the text to be cataloged, which has been retrieved at Step302. A text identifier is a number used for uniquely identifying aspecific text in a text database.

At Step 304, the text-structure analyzing program 210 is executed withthe selected text to be cataloged serving as an input thereto. Thetext-structure analyzing program 210 generates already-analyzed-textdata for the text to be cataloged, and stores the already-analyzed-textdata in the already-analyzed-text-data storing area 217.

At Step 305, the structure-index creating program 211 is executed, usingthe already-analyzed-text data generated at Step 304 as an inputthereto. First of all, the structure-index creating program 211retrieves a current structure index from the structure-index storingarea 218, cataloging structure information included in thealready-analyzed-text data in the structure index in order to update thestructure index. The updated structure index is then stored back in thestructure-index storing area 218.

At Step 306, the structured-full-text-data generating program 212 isexecuted, using the already-analyzed-text data generated at Step 304 asan input thereto. The structured-full-text-data generating program 212generates structured-full-text data for a text to be cataloged which hasbeen retrieved at Step 303, by referencing the already-analyzed-textdata, and stores the structured-full-text data in thestructured-full-text-data storing area 219.

At Step 307, the character-string-index creating program 213 is executedby using the structured-full-text data generated at Step 306 as an inputthereto. First of all, the character-string-index creating program 213retrieves a current character-string index from thecharacter-string-index storing area 220. The character-string-indexcreating program 213 then generates data representing an associativerelation between each partial string of characters having apredetermined length and structured-character-position information forthe partial string of characters from the structured-full-text data, andcatalogs the data in the character-string index retrieved from thecharacter-string-index storing area 220, updating the character-stringindex. The updated character-string index is then stored back in thecharacter-string-index storing area 220.

After the series of pieces of processing of Steps 302 to 307 have beencompleted for all the texts to be cataloged, the text-cataloging controlprogram 214 executes Step 308, ending the processing. At Step 308, thetext-cataloging control program 214 transmits all pieces ofalready-analyzed-text data stored in the already-analyzed-text-datastoring area 217, the structure index stored in the structure-indexstoring area 218, as well as the character-string index stored in thecharacter-string-index storing area 220 to the text searching server 102by way of the network 105.

The following is a description of details of the processing carried outat Step 304 of the procedure shown in FIG. 3, that is, a procedurecarried out by the text-structure analyzing program 210.

The text-structure analyzing program 210 carries out structure-analysisprocessing on a text to be cataloged. The text is an object ofprocessing which is written in SGML. In SGML, a logical structure commonto a group of texts pertaining to a specific type is defined in a DTD(Document Type Definition) format. FIG. 4 is a diagram showing anexample of the DTD. The DTD defines a logical structure of a text bydefining a set of logical elements composing the text. The logicalelements are each referred to hereafter simply as “elements”. A portiondelimited by a string of characters “<!ELEMENT” and the specialcharacter “>” is called an “element-type declaration”. An element-typedeclaration prescribes a name and a structure of a group of elements ofan element type. The name of such a group is referred to as an“element-type name”. The string of characters on the left-hand side ofan element-type declaration is an element-type name, whereas the portionon the right-hand side is a definition of the contents of the group ofelements.

In the DTD shown in FIG. 4, the element-type declaration on the top linedeclares the element type (“thesis”) and that a list of elementspertaining to this element type includes “title”, “author”, “date”,“main text”, and “list of references”, prescribing that the element typehas a structure wherein the elements pertaining to the element type arearranged with one element following another in the order enumerated onthe list, with no repetition of the same element. In the element-typedeclaration on the top line, the list of elements includes a pluralityof elements arranged in an order by delimiting one element from anotherby the special character comma (,) to indicate that the elementspertaining to the element type must appear in the same order in whichthe elements are enumerated on the list, with no repetition of the sameelement. These elements on the list are each declared as an element-typename in an element-type declaration that follows.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “author” prescribe astructure comprising one or more repeated elements pertaining to theelement type “name”. Literally, the right-side portion comprises theelement-type name “name” followed by the special character “+” toindicate that one or more elements pertaining to the element-type name“name” will appear.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “main text” prescribe astructure comprising none or one or more repeated elements pertaining tothe element type “chapter”. Literally, the right-side portion comprisesthe element-type name “chapter” followed by the special character “*” toindicate that either none or one or more elements pertaining to theelement-type name “chapter” will appear.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “chapter” prescribe astructure comprising one element pertaining to the element type “titleof the chapter” followed by either none or one or more repeated elementspertaining to the element type “comment” or “remark”, and then followedby either none or one or more repeated elements pertaining to theelement type “paragraph”. The special character pipe (“|”), used as adelimiter between two element-type names in a description of an element,indicates that the element represented by the two element-type namessandwiching the special character “|” pertains to either of the twoelement types indicated by the two element-type names. In a word, thespecial character “|” has the same meaning as the word “or”.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “paragraph” prescribe astructure comprising one element pertaining to the element type “titleof the paragraph” followed by either none or one or more repeatedelements pertaining to the element type “comment” or “remark”, and thenfollowed by either none or one or more repeated elements pertaining tothe element type “section”.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “section” prescribe astructure comprising one element pertaining to the element type “titleof the section” followed by either none or one or more repeated elementspertaining to the element type “comment” or “remark”.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “list of references”prescribe a structure comprising one or more repeated elementspertaining to the element type “reference”.

The contents of the element portion on the right-hand side of anelement-type declaration of the element type “reference” declare a listof elements pertaining to this element type, including “title”,“author”, “date”, and “description”, with no repetition of the sameelement on the list, and by delimiting one element from another by thespecial character comma, prescribing that the element type “reference”has a structure wherein the elements pertaining to the element type arearranged with one element following another in the order in which theyare enumerated on the list.

In addition, the contents of an element pertaining to the element type“title”, “name”, “date”, “title of the chapter”, “title of theparagraph”, or “title of the section” is prescribed merely as “#PCDATA”,indicating that the element is a lowest-level element which does nothave a sub-structure. That is to say, the contents of the element aresimply a string of characters. As for the element-type declaration ofthe element types “comment” and “remark”, an element pertaining toeither of these element types is either an element pertaining to anelement type “emphasis” or has a structure simply comprising a string ofcharacters. Since the declaration includes the special character “*”,the element can be none or one or more repeated element types “emphasis”or character strings.

A portion delimited by a string of characters “<!ATTLIST” and thespecial character “>” in the DTD shown in FIG. 4 is called anattribute-list declaration. An attribute-list declaration defines anattribute common to a group of elements pertaining to the same elementtype. In the DVD shown in FIG. 4, elements pertaining to the elementtype “remark” have a common attribute “type”. The value of the attribute“type” can be either “comparison” or “note”. When not specified, adefault value “references” is assumed.

An example of an SGML text written in accordance with the DTD shown inFIG. 4 is shown in FIG. 5. A portion delimited by a string of characters“<!DOCTYPE” and the special character “>” on the top line is called atext-type declaration for declaring the DTD followed in writing the SGMLtext and the element-type name of the element at the highest level.According to the prescription of the text-type declaration, the SGMLtext is written in accordance with a DTD stored in a file named“ronbun.dtd” and the element-type name of the element at the highestlevel is “thesis”. Here, the DTD stored in the file named “ronbun.dtd”is shown in FIG. 4.

As shown in FIG. 5, by adding marks for indicating the start and endpositions of each individual element of a text written in SGML, thestructure of the text can be revealed clearly. The marks for indicatingthe start and end positions of an individual element are referred to as“start tags” and “end tags”, respectively. A start tag preceding anelement is the element-type name of the element put between the specialcharacters “<” and “>”. On the other hand, an end tag succeeding anelement is the element-type name of the element sandwiched by a stringof special characters “</” and the special character “>”. If the elementhas an attribute, the name of the attribute can be prescribed in thestart tag thereof after the name of the element type. The value of theattribute is prescribed after the name of the attribute by putting theequal sign “=” between the name and the value of the attribute. In thecase of a start tag “<remark type=note>” shown in the SGML text of FIG.5, for example, the name of the element type is “remark”, the name ofthe attribute is “type”, and the value of the attribute is “note”. Aportion prescribing a text structure by using these tags in an SGML textis called a text instance.

FIG. 7 is a PAD showing details of the processing carried out at Step304 of the procedure shown in FIG. 3, which is carried out by thetext-structure analyzing program 210 of the present embodiment.

As shown in FIG. 7, the processing procedure begins with Step 701, atwhich, as the text-structure analyzing program 210 is activated to inputa text to be cataloged written in SGML, the text-structure analyzingprogram 210 reads in a text-type declaration described at the head ofthe text and analyzes the syntax thereof. The flow then goes on to Step702 to form a judgment as to whether a syntax error exists in thetext-type declaration. If a syntax error is found, the flow proceeds toStep 703 to output an error message, terminating the processing.

If a syntax error is not detected in the text-type declaration, on theother hand, the flow continues to Step 704 to form a judgment as towhether a DTD file is specified in the text-type declaration. If a DTDfile is not specified in the text-type declaration, the flow proceeds toStep 705 to output an error message, terminating the processing.

If a DTD file is specified in the text-type declaration, on the otherhand, the flow continues to Step 706, at which the contents of the DTDfile are retrieved and its syntax is analyzed. The flow then continuesto Step 707 to form a judgment as to whether a syntax error exists inthe DTD. If a syntax error is found, the flow proceeds to Step 708 tooutput an error message, terminating the processing. If a syntax erroris not detected in the DTD, on the other hand, the flow continues toStep 709, at which a text-structure table, containing data describing atext structure model defined by the DTD, is generated in a memory.

The flow then goes on to Step 710 to read in a text instance whilereferencing the text-structure table in order to analyze the structure.As a result, already-analyzed-text data is generated. Then, the flowproceeds to Step 711 to form a judgment as to whether a text instanceincludes a syntax error or a structure error (that is, a deviation fromthe structure model defined by the DTD). If a syntax error or astructure error exists in the text instance, the flow continues to Step712 to output an error message, terminating the processing. If a syntaxerror or a structure error is not found in the text instance, on theother hand, the flow continues to Step 713, at which thealready-analyzed-text data (comprising a text identifier for identifyingthe text to be cataloged) and analysis results obtained from thestructure analysis carried out at Step 710 were stored in thealready-analyzed-text-data storing area 217, and the processing isended.

As an example, the following describes a case in which thetext-structure analyzing program 210 is executed with the SGML text ofFIG. 5 used as a text to be cataloged and a DTD file named “ronbun.dtd”contains the DTD shown in FIG. 4. In this case, the text-structure tablegenerated at Step 709 has a data structure like that shown in FIG. 8.

As shown in FIG. 8, the text-structure table comprises two portions: astructure definition and an attribute definition. Associated with theelement-type names of the element types composing the DTD, the structuredefinition defines a data model of possible contents of an elementpertaining to each element type. Also associated with the element-typenames of the element types composing the DTD, the attribute definitiondefines the name, the type of the value, and the default value of anattribute owned by an element pertaining to each element type. Byreferring to the structure definition, it is possible to form a judgmentas to whether the order of arrangement and the hierarchical relation ofa group of elements appearing in a text instance are correct (that is,to form a judgment as to whether a structure error exists), and to addinformation on tags and an attribute-value specification in case theyhave been omitted.

With the text-structure analyzing program 210 executed with the SGMLtext of FIG. 5 used as the input text to be cataloged and a DTD filenamed “ronbun.dtd” containing the DTD shown in FIG. 4,tree-like-structure data shown in FIG. 6 is obtained asalready-analyzed-text data. FIG. 6 is a model diagram showingdiagrammatically the logical structure of the text written in SGML asshown in FIG. 5. As shown in FIG. 6, the logical structure of astructured text can be regarded to have a tree-like structure withindividual elements of the logical structure serving as intermediatenodes and pieces of character-string data serving as end nodes. In thetree-like structure shown in FIG. 6, an element is represented by anellipse while a string of characters is shown as a rectangle.

In the embodiment described above, a structured text described in SGMLis processed as a text to be cataloged. However, the present inventioncan also be applied to a configuration wherein a structured textdescribed in another format such as an ODA (Open Document Architecture)is processed as a text to be cataloged.

FIG. 9 is a PAD showing details of the processing carried out at Step305 of the procedure shown in FIG. 3 (that is, a procedure carried outby the structure-index creating program 211 of the present embodiment).

As shown in FIG. 9, the processing procedure begins with Step 901, atwhich the structure-index creating program 211 forms a judgment as towhether a structure index already exists in the structure-index storingarea 218. If no structure index exists in the structure-index storingarea 218 yet, the flow goes on to Step 902, at which the structure-indexcreating program 211 creates an initial-state (or empty) structureindex. If a structure index already exists in the structure-indexstoring area 218, on the other hand, the flow proceeds to Step 903, atwhich the structure-index creating program 211 retrieves the structureindex from the structure-index storing area 218.

The flow then continues to Step 904, at which the structure-indexcreating program 211 retrieves the already-analyzed-text data of thetext to be cataloged from the already-analyzed-text-data storing area217.

Then, the flow goes on to Step 905, at which the structure-indexcreating program 211 searches the already-analyzed-text data for allnodes, that is, elements and pieces of character-string data, which formthe tree-like structure of the already-analyzed-text data. Pieces ofprocessing of Steps 906 to 909 are repeated with the each of the nodestreated as an object of processing.

At Step 906, the structure-index creating program 211 forms a judgmenton a node of the already-analyzed-text data currently being processed(that is, a judgment as to whether a metanode associated with the nodeexists in the structure index). A metanode is either a metaelement or apiece of meta-character-string data. If a metanode associated with thenode does not exist in the structure index, the flow goes on to Step907, at which a metanode is created and cataloged in the structureindex. The flow then proceeds to Step 908, at which a context identifieris assigned to the cataloged metanode. A context identifier is a numberused for uniquely identifying a metanode in the structure index. Then,the flow continues to Step 909, at which the structure-index creatingprogram 211 adds an associative relation between a node in thealready-analyzed-text data currently being processed and the contextidentifier uniquely identifying the cataloged metanode in the structureindex associated with the node to the already-analyzed-text data,updating the already-analyzed-text data.

After Steps 906 to 909 have been repeated for all nodes, the flowcontinues to Step 910, at which the updated already-analyzed-text datais output and stored in the already-analyzed-text-data storing area 217.Then, the flow proceeds to Step 911, at which the updated structureindex is output and stored in the structure-index storing area 218, andthe structure-index creating program 211 ends the processing.

When carrying out the pieces of processing at Steps 906 to 909repeatedly, by treating each node composing the tree-like structure ofthe already-analyzed-text data as an object, the individual nodes of thetree-like structure are processed by tracing the tree-like structure inan order to be explained by referring to FIG. 10.

In this figure, an ellipse represents an element node, whereas arectangle represents a character-string node. If a node has a pluralityof lower-level nodes directly subordinate to the node, the lower-levelnodes are represented by arranging them from the left to the right inthe order in which they appear in the already-analyzed-text data. Anumber shown inside a node is a processing order number of the node. Asshown in this figure, the order in which a group of nodes are processedat Steps 906 to 909 starts with a node located at the root of thetree-like structure. In addition, the order of processing of a specificnode and a group of lower-level nodes directly subordinate to thespecific node starts with the specific node, to be followed byprocessing of the lower-level nodes in the order they appear in thetree-like structure, beginning with the left-most directly subordinatenode.

The following is a description of details of the processing carried outat Step 906 on a node of the already-analyzed-text data that iscurrently being processed to form a judgment as to whether a metanodeassociated with (or mutually corresponding to) the node exists in thestructure index, with reference to FIG. 11. FIG. 11 is a diagram showingan associative relation between a group of nodes composing the tree-likestructure of the already-analyzed-text data shown on the left-hand sideof the figure, and a group of nodes (strictly speaking, metanodes)composing the tree-like structure of the structure index created for thealready-analyzed-text data shown on the right-hand side of the figure.

Here, in the present embodiment, a node in already-analyzed-text dataand a metanode in a structure index created for thealready-analyzed-text data are defined to be associated with (orcorresponding to) each other if the tree-like-structure address of thenode in the tree-like structure of the already-analyzed-text data is thesame as the tree-like-structure address of the metanode in the tree-likestructure of the structure index created for the already-analyzed-textdata. A tree-like-structure address of a particular node in a tree-likestructure is a series of pairs of codes which are determined whentracing a path in the tree-like structure starting from the root of thetree-like structure and ending at the particular node in order ofdescending node level. Each pair of codes represents a node encounteredin the traced path.

The first code in each pair indicates the type of the node. Moreparticularly, the first code indicates whether the node is an element ora piece of character-string data and, if the node is an element, thefirst code also indicates the type of the element. The second code ineach pair is an appearance-order number of the node in a tree-likestructure among brother nodes, which are nodes pertaining to the sametype in the tree-like structure. The pairs of codes are arranged in thesame chronological order in which the respective nodes are encounteredalong the traced path. A tree-like-structure address of a metanode inthe tree-like structure of a structure index is defined in the same wayas a node in the tree-like structure of already-analyzed-text data.

A group of nodes composing the already-analyzed-text data shown on theleft-hand side of FIG. 11 can be taken as an example from which thetree-like-structure addresses of some nodes in the tree-like structurecan be found. As shown in this figure, a node 1101 in the group is theroot node in the tree-like structure which does not have a node directlysuperordinate thereto.

The tree-like-structure address of a node 1104 is found by tracing thetree-like structure of the already-analyzed-text data, starting from theroot node 1101. Since the node 1101 is a first one among brother nodespertaining to the an element node “thesis”, the tree-like-structureaddress of the node 1101 is “/thesis[1]”. Tracing the tree-likestructure further, a node 1102 is found directly subordinate to the node1101. In addition, the node 1102 is a first one among brother nodespertaining to the element node “chapter”. Thus, the tree-like-structureaddress of the node 1102 is “/thesis[1]/chapter[1]”.

By the same token, the tree-like-structure address of a node 1103 can bedescribed as “/thesis[1]/chapter[1]/paragraph[2]”. This is because thenode 1103 is directly subordinate to the node 1102 and a second oneamong brother nodes pertaining to the an element node “paragraph”.Likewise, the tree-like-structure address of a node 1104 can bedescribed as “/thesis[1]/chapter[1]/paragraph[2]/comment[1]”. This isbecause the node 1104 is directly subordinate to the node 1103 and afirst one among brother nodes pertaining to the an element node“comment”.

Tree-like-structure addresses of metanodes composing the tree-likestructure of the structure index shown on the right-hand side of FIG. 11are found in the same way as nodes in the already-analyzed-text data onthe left-hand side of the figure as follows. The tree-like-structureaddress of a metanode 1105 is “/thesis[1]” which is the same as that ofthe node 1101. Similarly, the tree-like-structure address of a metanode1106 is “/thesis[1]/chapter[1]” which is the same as that of the node1102, and the tree-like-structure address of a metanode 1107 is“/thesis[1]/chapter[1]/paragraph[2]”, which is the same as that of thenode 1103. Thus, the metanodes 1105, 1106, and 1107 are judged to beassociated with (or to mutually correspond to) the nodes 1101, 1102, and1103, respectively, at Step 906 of the processing procedure shown inFIG. 9.

Since the structure index shown in FIG. 11 does not include a metanodethat has the same tree-like-structure address as the node 1104 of thealready-analyzed-text data, the node 1104 is judged not to have ametanode associated with (or mutually corresponding to) it in thestructure index. Thus, a new metanode associated with the node 1104 iscreated and cataloged in the structure index at Step 907. A new metanodeassociated with (or mutually corresponding to) a node is cataloged inthe structure index at Step 907 by adding the new metanode to the end ofa group of metanodes directly subordinate to a higher-level metanodeassociated with (or mutually corresponding to) a higher-level nodedirectly superordinate to the node, and assigning a type correspondingto the type of the node to the new metanode. Thus, in the case of thenode 1104, a new metanode associated with the node 1104 is cataloged inthe structure index at Step 907 by adding the new metanode to the end ofa group of metanodes directly subordinate to the higher-level metanode1107 associated with (or mutually corresponding to) the higher-levelnode 1103 directly superordinate to the node 1104, and assigning thetype “comment” corresponding to the type of the node 1104 to the newmetanode.

The following is description of a process to develop a structure indexby sequentially superposing a plurality of pieces ofalready-analyzed-text data one after another, with reference to FIG. 12.In this figure, reference numerals 1201, 1203, and 1205 each denote apiece of already-analyzed-text data of a text to be cataloged. Thetree-like structures of the pieces of already-analyzed-text data aresequentially superposed one-by-one on the structure index, in theprocess of developing the structure index.

First of all, when the already-analyzed-text data 1201 of Text 1 isinput at an initial stage, the structure index is in an initial (orempty) state. In this case, a tree-like structure equivalent to that ofthe already-analyzed-text data 1201 is cataloged in the structure index,which has the state denoted by reference numeral 1202. At this time,context identifiers E1, E2, E3, E4, and E5 are assigned to metaelementsthat are newly created in the structure index 1202, whereas contextidentifiers C1, C2, and C3 are assigned to newly created pieces ofmeta-character-string data.

Next, when the already-analyzed-text data 1203 of Text 2 is input, nodesin the tree-like structure of the already-analyzed-text data 1203overlapping those of the existing structure index 1202 are notprocessed. In other words, only nodes in the tree-like structure of thealready-analyzed-text data 1203 that have no mutually correspondingmetanodes in the existing structure index 1202 (that is, only hatchednodes in the tree-like structure of the already-analyzed-text data 1203)are newly cataloged in the structure index 1202. At this time, contextidentifiers E6 and E7 are assigned to newly-cataloged metaelements inthe structure index 1202, whereas a context identifier C4 is assigned toa newly-cataloged piece of meta-character-string data, resulting in thestructure index state denoted by reference numeral 1204.

Similarly, when the already-analyzed-text data 1205 of Text 3 is theninput, nodes in the tree-like structure of the already-analyzed-textdata 1205 that overlap those of the existing structure index 1204 arenot processed. In other words, only nodes in the tree-like structure ofthe already-analyzed-text data 1205 that have no mutually correspondingmetanodes in the existing structure index 1204 (that is, only hatchednodes in the tree-like structure of the already-analyzed-text data 1205)are newly cataloged in the structure index 1204. At this time, contextidentifiers E8, E9, and E10 are assigned to newly-cataloged metaelementsin the structure index 1204, whereas context identifiers C5 and C6 areassigned to newly-cataloged pieces of meta-character-string data. Thestructure index state 1206 results upon completion of the cataloging ofthe three pieces of already-analyzed-text data 1201, 1203, and 1205 hasbeen completed.

FIG. 13 is a PAD showing details of the processing carried out at Step306 of the procedure shown in FIG. 3, that is, a procedure carried outby the structured-full-text-data generating program 212 of the presentembodiment.

As shown in FIG. 13, the procedure begins with Step 1301, at which thestructured-full-text-data generating program 212 retrieves thealready-analyzed-text data of a text to be cataloged from thealready-analyzed-text-data storing area 217.

The flow then goes on to Step 1302, at which a text identifier foridentifying a text to be cataloged is output to thestructured-full-text-data storing area 219.

Then, the flow proceeds to Step 1303, at which thestructured-full-text-data generating program 212 searches thealready-analyzed-text data for all nodes (that is, elements and piecesof character-string data) which form the tree-like structure of thealready-analyzed-text data. Pieces of processing of Steps 1304 to 1306are repeated, with each node treated as an object of processing.

At Step 1304, the structured-full-text-data generating program 212 formsa judgment as to whether a node of the already-analyzed-text datacurrently being processed is an element or character-string data. Onlyif the node of the already-analyzed-text data currently being processedis character-string data does the flow continue to Step 1305, at which acontext identifier assigned to the character-string data currently beingprocessed is found from the already-analyzed-text data and output to thestructured-full-text-data storing area 219. The flow then goes on toStep 1306, at which a descriptive complete string of characters of thenode representing the character-string data currently being processed isoutput to the structured-full-text-data storing area 219.

When the pieces of processing of Steps 1304 to 1306 have been repeatedfor all of the nodes, the structured-full-text-data generating program212 ends.

FIG. 14 is a diagram showing a format in which structured-full-text datais output by the structured-full-text-data generating program 212 to afile. FIG. 14 exemplifies a case in which the structured-full-text datais generated from the SGML text shown in FIG. 5. As shown in FIG. 14,the format of the file for storing the structured-full-text data adoptedin the present embodiment starts with a text identifier, followedrepetitively by as many pairs of a context identifier and a descriptivecomplete string of characters associated with the context identifier aspieces of character-string data existing in the text.

For example, the text identifier D1 identifies a text to be cataloged bythe structured-full-text data shown in FIG. 14, and a context identifierC5 is assigned to character-string data described as the contents of a“date” element shown in FIG. 5. These identifiers are each expressed bya symbol in FIG. 14 and in other diagrams for simplicity of explanation.It should be noted, however, that a text identifier is actually a number(strictly speaking, an integer) recorded in data for uniquelyidentifying a specific text among a group of texts to be cataloged,whereas an actually recorded context identifier is also a number(strictly speaking, an integer) for uniquely identifying a specificmetanode among a group of metanodes composing a structure index.

FIG. 15 is a PAD showing details of Step 307 (FIG. 3), which is carriedout by the character-string-index creating program 213 of the presentembodiment.

At Step 1501, the character-string-index creating program 213 forms ajudgment as to whether a character-string index already exists in thecharacter-string-index storing area 220. If no character-string indexexists yet in the character-string-index storing area 220, the flow goeson to Step 1502, at which the character-string-index creating program213 creates an initial-state (or empty) character-string index. If acharacter-string index already exists in the character-string-indexstoring area 220, on the other hand, the flow proceeds to Step 1503, atwhich the character-string-index creating program 213 retrieves thecharacter-string index from the character-string-index storing area 220.

The flow then continues to Step 1504, at which thecharacter-string-index creating program 213 retrieves thestructured-full-text data of the text to be cataloged from thestructured-full-text-data storing area 219.

Then, the flow goes on to Step 1505, at which the character-string-indexcreating program 213 searches the structured-full-text data for alldescriptive complete character strings. Pieces of processing of Steps1506 and 1507 are repeated, with all descriptive complete characterstrings each being treated as an object of processing.

At Step 1506, the character-string-index creating program 213 extractspartial character strings, each of which has a predetermined length,from a descriptive complete string of characters in thestructured-full-text data currently being processed. The flow then goeson to Step 1507, at which an associative relation between each of thepartial character strings extracted at Step 1506 andstructured-character-position information of the partial characterstrings is cataloged in the character-string index.

After the pieces of processing carried out at Steps 1506 and 1507 havebeen completed for all of the descriptive complete character strings,the flow proceeds to Step 1508 to delete and discard thestructured-full-text data, which became no longer necessary, from thestructured-full-text-data storing area 219. Then, the flow of theprocessing procedure continues to Step 1509, at which the updatedcharacter-string index is output and stored in thecharacter-string-index storing area 220.

When a partial string of characters having a predetermined length isextracted from a certain descriptive complete string of characters atStep 1506, as described above, the number of characters to be extractedis determined by the length (the character count) of the partial stringof characters to be extracted, which is determined in advance. A groupof partial character strings, each having a character count determinedin advance, is then extracted from the descriptive complete string ofcharacters sequentially, one partial string after another. Theextraction begins with a partial string of characters at the head of thedescriptive complete string of characters, and proceeds while shiftingthe extracted position one character at a time, until the last partialstring of characters of the descriptive complete string of characters isextracted. For example, considering a partial string having a length(character count) of 2 characters, and “an example of transformation” asthe descriptive complete string of characters (the object to beprocessed) identified by a context identifier C129 from which a group ofpartial character strings each having the character count are to beextracted, 27 partial character strings can be extracted: “an”, “n_”,“_e”, “ex”, “xa”, “am”, “mp”, “pl”, “le”, “e_”, “_o”, “of”, “f_”, “_t”,“tr”, “ra”, “an”, “ns”, “sf”, “fo”, “or”,“rm”, “ma”, “at”,“ti”,“io”, and“on”.

As for the end portion of a descriptive complete character string, thenumber of characters in the length of a partial string of characters(the character count), minus one, are further extracted. In the case ofthe descriptive complete string, “an example of transformation”, thelast character “n” is further extracted from the end portion thereof.When the extracted partial character strings extracted at Step 1506 arecataloged in the character-string index at Step 1507, an associativerelation between each of the partial character strings and thestructured-character-position information of the partial characterstrings showing the positions of the partial character strings in thedescriptive complete string of characters, is also cataloged in thecharacter-string index. Here, the structured-character-positioninformation associated with a partial string of characters comprises thetext identifier of a text including the partial character string, acontext identifier identifying the descriptive complete string ofcharacters including the partial character string (that is, identifyinga position in the text of the character-string data including thepartial string of characters), and a number identifying a position ofthe head character of the partial string of characters in thedescriptive complete character string.

FIG. 16 is a diagram showing the data structure of a character-stringindex used in the present embodiment. More particularly, FIG. 16 showsonly a portion of the data structure of a character-string index,obtained at a stage where an operation to catalog a group of partialcharacter strings included in the structured-full-text data into thecharacter-string index has been completed, at the end of the processingof the structured-full-text data carried out by thecharacter-string-index created program 213. The portion of the datastructure of the character-string index corresponds to the descriptivecomplete string of characters “an example of transformation” describedabove. It should be noted, however, that the character node for the lastcharacter “n” of the descriptive complete string of characters and thestructured-character-position information for the last character areomitted from the portion of the data structure of the character-stringindex shown in FIG. 16. In addition, the position of the head characterof a partial string of characters in the descriptive complete string ofcharacters is expressed as a position relative to X, the position of acharacter immediately preceding the descriptive complete characterstring.

As shown in FIG. 16, the character-string index is used for holding alist of pieces of appearance position information (that is, a list ofpieces of the structured-character-position information described above)for each partial character string appearing in a text to be catalogedwith a predetermined character count. As described above, each piece ofstructured-character-position information comprises a text identifier, acontext identifier, and a number indicating the position of the headcharacter in a partial character string. In order to increase the speedof searching the character-string index, the character-string indexadopts a data structure in which, for a group of partial characterstrings having a common first character, information on the first commoncharacter is made common to and shared by all the partial characterstrings pertaining to the group. In addition, pointers pointing to nodesof first characters from the root of the character-string index arearranged in the order the codes of the first characters pointed to bythe pointers are arranged. By the same token, pointers pointing to nodesof second characters from a node of a first character are arranged inthe order the codes of the second characters pointed to by the pointersare arranged.

By processing all texts to be cataloged in a text database andcataloging a group of partial character strings appearing in the textsinto a character-string index as described above, it is possible to knowthe position of and text containing a string of characters comprisingany two characters merely by referencing the character-string index,without the need to scan the text data itself at all. A method forsearching the text database for a string of characters having a lengthother than two characters will be described later.

In the present embodiment, the predetermined length (the charactercount) of the partial string of characters is two. It should be noted,however, that a similar character-string index can also be constructedwith a character count set at a value other than two. In addition, eventhough the predetermined character count of the partial string ofcharacters in the present embodiment is fixed, a similarcharacter-string index can be constructed as well with a variablecharacter count.

At this point, the explanation of the text cataloging sub-system 101implemented by the present embodiment is completed.

The following is description of the text searching server implemented bythe first embodiment of the present invention, that is, the apparatusdenoted by reference numeral 102 in FIG. 1.

FIG. 17 is a diagram showing the configuration of a text searchingserver 102 implemented by the present embodiment.

As shown in this figure, the text searching server 102 comprises adisplay unit 201, a keyboard 202, a central processing unit (CPU) 203, afloppy-disk drive 204, a floppy disk 205, a communication controlapparatus 206, a main memory unit 207, a magnetic-disk drive 208, and asystem bus 209.

The display unit 201 is used for displaying information such as anexecution state of processing carried out in the text catalogingsub-system 101, and the keyboard 202 is used for entering a commandmaking a request for an operation such as the activation and the haltingof the text searching server 102. The central processing unit 203executes a variety of programs constituting the functions of the textsearching server 102. The communication control unit 206 is used forcommunicating with the text cataloging sub-system 101 and the textsearching clients 103 and 104 through the network 105, in order toexchange requests and data with the text cataloging sub-system 101 andthe text searching clients 103 and 104.

The main memory unit 207 is used for storing a variety of programs to beexecuted for carrying out various kinds of processing of the textsearching server 102, and for holding data temporarily. Themagnetic-disk drive 208 is used for storing text data in a text databaseand index data referenced by the text searching server 102. The systembus 209 is used for connecting the display unit 201, the keyboard 102,the central processing unit (CPU) 203, the communication controlapparatus 206, the main memory unit 207, and the magnetic-disk drive 208with each other.

Including also a work area 216, the main memory unit 207 is used forstoring a search-condition analyzing program 1701, acharacter-string-index searching program 1702, a text-search controlprogram 1703, and a system program 215. The magnetic-disk drive 208stores an already-analyzed-text-data storing area 217, a structure-indexstoring area 218, a character-string-index storing area 220, and asearch-result-data storing area 1704.

The search-condition analyzing program 1701 analyzes a search-conditionequation included in a request for a search operation received from thetext searching client 103 or 104, and translates the search-conditionequation into a condition specification that can be readily searched bythe character-string-index searching program 1702. Thecharacter-string-index searching program 1702 searches thecharacter-string index stored in the character-string-index storing area220 for desired information in accordance with the conditionspecification resulting from the translation carried out by thesearch-condition analyzing program 1701. Search-result data obtainedfrom the search operation (that is, the desired information) is storedin the search-result-data storing area 1704.

The text-cataloging control program 1703 controls the activation and theexecution of the search-condition analyzing program 1701 and thecharacter-string-index searching program 1702. The text-searchingcontrol program 1703 also exchanges requests and data with the textcataloging sub-system 101 and the text searching clients 103 and 104 byway of the network 105. The system program 215 provides basic functionsfor executing the programs implementing the functions of the textsearching server 102 on the computer. The basic functions includeinputting and outputting data from and to peripheral devices. The workarea 216 is used for storing data required temporarily in the executionof the programs.

As described above, in the present embodiment, the text-searchingcontrol program 1703 exchanges requests and data with the textcataloging sub-system 101 and the text searching clients 103 and 104 byway of the network 105. However, it is also possible to build aconfiguration wherein another portable medium such as the floppy disk205, an optical magnetic disk, or a writable optical disk is used inplace of the network 105. As an alternative, it is also possible tobuild a configuration wherein the text cataloging sub-system 101 and thetext searching server 102 are implemented by a single computer so thatno data transfers are needed between the text cataloging sub-system 101and the text searching server 102. As another alternative, it is alsopossible to build a configuration wherein one or more text searchingclients and the text searching server 102 are implemented by a singlecomputer so that no data transfers are needed between the text searchingclients and the text searching server 102.

FIG. 18 is a PAD showing a procedure for searching a text adopted by thefirst embodiment of the present invention. When the text-searchingcontrol program 1703 is invoked, typically by a server invoking acommand entered via the keyboard 202, the program executes a function ofthe text searching server 102 to receive a request transmitted from thetext cataloging sub-system 101 or the text searching client such as thatdenoted by reference numeral 103 or 104, getting in a processingperforming loop at Step 1801. The loop is continued until a request tohalt the processing is entered via the keyboard 202.

At Step 1801, the processing of Step 1802 to receive a requesttransmitted from the text cataloging sub-system 101 or the textsearching client 103 or 104, and processing of Step 1803 to determinethe type of the request and to make a decision as to which step tobranch to in accordance with the type of the request, are repeated.

If a result of the determination of the request type at Step 1803indicates that the request is a data-base-update request received fromthe text cataloging sub-system 101, the flow goes on to Step 1804 andthen to Step 1805. A data-base-update request is a request to update thedatabase by cataloging a group of new texts.

If a result of the determination of the request type at Step 1803indicates that the request is for a text search transmitted by a textsearching client such as that denoted by reference numeral 103 or 104,the flow proceeds to pieces of processing carried out at Steps 1806 to1808. A request for a text search is a request for an operation tosearch the database for a group of texts that satisfy a specific searchcondition. If a result of the determination of the request type at Step1803 indicates that the request is a search-result inquiring requesttransmitted by a text searching client such as that denoted by referencenumeral 103 or 104, the flow proceeds to Step 1809. A search-resultinquiring request is a request to make an inquiry about a specificsearch result.

If a result of the determination of the request type at the step 1803indicates that the request is a text-transfer request transmitted by atext searching client such as that denoted by reference numeral 103 or104, the flow proceeds to Step 1810. A text-transfer request is arequest for a transfer of specified text data. After the processingcarried out at Step 1805, 1808, 1809, or 1810 (the destination step ofthe branch from Step 1803) has been completed, the processing returns toStep 1802.

At Step 1804, already-analyzed-text data of a newly cataloged text groupis received from the text cataloging sub-system 101 and added to dataalready stored in the already-analyzed-text-data storing area 216. Theflow then goes on to Step 1805, at which an updated character-stringindex and an updated structure index reflecting the contents of thenewly cataloged text group are received from the text catalogingsub-system 101 and added to a character-string index and a structureindex already existing in the character-string-index storing area 220and the structure-index storing area 218, respectively.

At Step 1806, the search-condition analyzing program 1701 is executed inorder to analyze a search condition included in a request for a searchoperation received from the text searching client 103 or 104, and totranslate the search condition into a condition specification that canbe readily searched by the character-string-index searching program1702. The condition specification is referred to hereafter as“already-developed-search-condition data”. The flow then proceeds toStep 1807, at which the character-string-index searching program 1702 isexecuted by treating the already-developed-search-condition datagenerated at Step 1806 as an input to search the database for a group oftexts that satisfy the condition specified by thealready-developed-search-condition data. Search-result data obtainedfrom the search operation is associated with a search-result identifierfor uniquely identifying the search-result data, and stored in thesearch-result-data storing area 1704. Then, the flow continues to Step1808, at which the search-result identifier is transmitted to the textsearching client that made the request for a text search.

At Step 1809, part or all of the search-result data obtained at Step1807 is retrieved from the search-result-data storing area 1704 inaccordance with the contents of the inquiry, and transmitted to the textsearching client that made the search-result inquiring request.

At Step 1810, already-analyzed-text data of a text specified in thetext-transfer request is retrieved from the already-analyzed-text-datastoring area 217 and transmitted to the text searching client that madethe text-transfer request. It should be noted that, if a plurality oftexts are specified in the text-transfer request, pieces ofalready-analyzed-text data of all texts are retrieved from thealready-analyzed-text-data storing area 217 and transmitted to the textsearching client that made the text-transfer request.

FIG. 19 is a PAD showing details of the procedure carried out at Step1806 shown in FIG. 18, which is a procedure of carried out by thesearch-condition analyzing program 1701 of the present embodiment.

As shown in FIG. 19, the procedure begins with Step 1901, at which thesearch-condition analyzing program 1701 is invoked by a request for atext search including a specified search condition as an input to theprogram, and forms a judgment as to whether the search conditionincludes a structure condition. Only if the search condition includes astructure condition are pieces of Steps 1902 and 1903 carried out. Ifthe search condition does not include a structure condition, however,the flow goes on to Step 1904.

At Step 1902, the structure index is retrieved from the structure-indexstoring area 218. The flow then proceeds to Step 1903, at which thestructure index is searched for a set of context identifiers of allpieces of character-string data included in the structure index whichsatisfies the structure condition. The set of context identifiers isreferred to hereafter as a “context-identifier set”.

At Step 1904, on the other hand, the search-condition analyzing program1701 forms a judgment as to whether the character count of a string ofcharacters specified as a character-string condition in the searchcondition exceeds the length of the partial string of characters whichwas determined in advance at the time the character-string index wascreated. If the character count of the string of characters exceeds thelength of the partial character string, the flow goes on to Step 1905,at which the search-condition analyzing program 1701 sequentiallyextracts a group of partial character strings, each having thepredetermined character count of two, from the specified string ofcharacters. The extraction starts with the partial string of charactersat the head of the specified string of characters, and proceeds whileshifting the extracted position by one character at a time until thelast partial string of characters of the specified string of charactersis extracted. Then, a list of partial character strings including theextracted partial character strings is generated as members thereof. Ifthe character count of a string of characters does not exceed thepredetermined length of the partial character string, on the other hand,the flow goes on to Step 1906, at which an empty list of partialcharacter strings including no members is created.

At Step 1907, the search-condition analyzing program 1701 generatesalready-developed-search-condition data comprising the set of contextidentifiers found at Step 1903, the specified string of charactersincluded in the search condition, and the list of partial characterstrings generated at Step 1905 or 1906, terminating the processing.

FIG. 20 is a diagram showing an example of generation of thealready-developed-search-condition data in processing carried out by thesearch-condition analyzing program 1701.

In this figure, reference numeral 2001 denotes an example of a searchcondition specified in a request for a text search. The search condition2001 comprises a specification of a structure condition“chapter/comment[1]” and a specification of a character-string condition“guard”. The search condition 2001 specifies a search of the structureindex to be carried out for a case in which the string of characters“guard” appears in the first element “comment”, which is directlysubordinate to the element “chapter”.

Assuming that the contents of the structure index are as shown byreference numeral 2002, the search of the structure index carried out atStep 1903 reveals that “comment” elements satisfying the specificationof the structure conditions have the context identifiers E5 and E14.Thus, pieces of character-string data directly subordinate to these“comment” elements (that is, pieces of character-string data with thecontext identifiers C3 and C9) must be searched for next when the stringof characters “guard” appears. In the character-string index to be usedin the search, however, only appearance positions of partial characterstrings each having a length of two characters are cataloged. Thus, adirect search for a specified string of three or more characters likethe string “guard ” cannot be carried out.

In order to solve this problem, the search-condition analyzing program1701 sequentially extracts a group of partial character strings, eachhaving the predetermined character count of two, from the specifiedstring of characters. The extraction starts with the partial string ofcharacters at the head of the specified string of characters, andproceeds while shifting the extracted position by one character at atime until the last partial string of characters of the specified stringof characters is extracted. The program then generates a list of partialcharacter strings including the extracted partial character strings asmembers thereof at Step 1905. In the case of the specified string ofcharacters “guard”, the list of partial character strings extracted fromthe specified string has partial string characters “gu”, “ua”, “ar”, and“rd” as its members.

As a result, already-analyzed-search-condition data 2003 comprising acontext-identifier set {C3, C9}, the specified string of characters“guard”, and a list of partial character strings {“gu”, “ua”, “ar”, and“rd”} as shown in FIG. 20 is generated at Step 1907 of the procedureshown in FIG. 19.

FIG. 21 is a PAD showing details of the procedure carried out at Step1807, which is carried out by the character-string-index searchingprogram 1702 of the present embodiment.

The character-string-index searching program 1702 is activated,inputting already-developed-search-condition data generated by thesearch-condition analyzing program 1701. When the character-string-indexsearching program 1702 is invoked, the character-string-index searchingprogram 1702 retrieves the character-string index from thecharacter-string-index storing area 220 at Step 2101 of the procedureshown in FIG. 21. The flow then goes on to Step 2102, at which thesearch-result data is initialized.

Then, the flow proceeds to Step 2103 to compare the character count of aspecified string of characters included in thealready-developed-search-condition data with the length of the partialstring of characters which was determined in advance at the time thecharacter-string index was created.

If the character count of the specified string of characters is found tobe equal to the length of the partial character string, the flow goes onto Step 2104. If the character count of the specified string ofcharacters is found to be smaller than the length of the partialcharacter string, on the other hand, the flow proceeds to Step 2105. Ifthe character count of the specified string of characters is found to begreater than the length of the partial character string, the flow goeson to Step 2106.

At Step 2104, the character-string index is searched for partialcharacter strings matching the specified string of characters, and a setof pieces of structured-character-position information corresponding tothe partial character strings are found. Then, only a group of pieces ofstructured-character-position information, each having a contextidentifier included in the set of context identifiers of thealready-developed-search-condition data, are extracted from the set ofpieces of structured-character-position information. Finally, a set ofbit positions composed of the extracted group of pieces ofstructured-character-position information is created.

Much like Step 2104, at Step 2105, the character-string index issearched for partial character strings matching the specified string ofcharacters, and a set of pieces of structured-character-positioninformation corresponding to the partial character strings are found. Inthis case, however, since the character count of the specified string ofcharacters is smaller than the length of a partial string of characters,the character-string index is searched for partial character strings,the front portion of each of which matches the specified string ofcharacters. The front portion of a partial string of characters is aportion starting with the head character and ending with a characternode corresponding to the end character of the specified string ofcharacters. Then, only a group of pieces ofstructured-character-position information, each of which has a contextidentifier included in the set of context identifiers of thealready-developed-search-condition data, are extracted from the group ofpieces of structured-character-position information. Finally, a set ofbit positions composed of the extracted group of pieces ofstructured-character-position information is created.

At Step 2106, Step 2107 is repeated for each partial character stringconstituting the list of partial character strings in thealready-developed-search-condition data. At Step 2107, thecharacter-string index is searched for a partial string of characters,and a set of pieces of structured-character-position informationcorresponding to the partial string of characters is found. Then, only agroup of pieces of structured-character-position information that have acontext identifier included in the set of context identifiers of thealready-developed-search-condition data are extracted from the set ofpieces of structured-character-position information. Finally, theextracted group of pieces of structured-character-position informationare stored by being associated with the partial string of characters.

When the repetitive processing of Step 2106 is completed, the flow goeson to Step 2108, at which a connection judging process is carried out oneach group of pieces of structured-character-position informationassociated with a partial string of characters, to concatenate partialcharacter strings. Then, as a concatenated string of characters, only aparticular group of pieces of structured-character-position informationassociated with partial character strings that match the specifiedstring of characters are extracted, and onlystructured-character-position information corresponding to the partialstring of characters at the head of the specified string of charactersin each of the particular groups is extracted as a representative of theparticular group. Finally, a set of bit positions composed of theextracted group of pieces of structured-character-position information(particularly, a set of bit positions composed of representatives of theparticular groups of pieces of structured-character-positioninformation) is created.

When Step 2104, 2105, or 2108 (that is, the last step of the destinationof the branch from Step 2103) has been completed, the flow proceeds toStep 2109, at which the group of pieces of structured-character-positioninformation included in the set of bit positions is organized intosub-groups, each comprising only those pieces ofstructured-character-position information having the same textidentifier, and cataloged in the search-result data.

The concatenation judging process, the processing of thecharacter-string-index searching program 1702 carried out at Step 2108,is described in more detail by referring to FIG. 22 as follows.

In this figure, reference numeral 2201 denotes an example (or a portion)of the character-string index. When the character-string index holdingthe data 2201 is searched in accordance with a condition shown by thealready developed search-condition data 2003 shown in FIG. 20, a groupof pieces of structured-character-position information for the partialcharacter strings “gu” and “ua” identified by context identifiers C3 andC9 are extracted as indicated by the step 2107. The extracted pieces ofinformation are then associated with the partial character strings toform data 2202. The concatenation judging process is carried out on thedata.

In the concatenation judging process carried out at Step 2108, thecharacter-string-index searching program 1702 forms a judgment as towhether a combination of concatenated partial character stringsrepresented by pieces of information in the extracted group that matchesthe whole specified string of characters exists. Such a combination mustsatisfy the following conditions:

(1) The pieces of structured-character-position information have thesame text identifier.

(2) The pieces of structured-character-position information have thesame context identifier.

(3) If the pieces of structured-character-position information arearranged in an order of increasing character-position values, and thenthe group of partial character strings represented by the pieces ofstructured-character-position information are arranged in the same orderof character position, as a whole, a string of characters equivalent tothe specified string of characters is obtained.

The example 2202 includes a combination which, as a whole, composes thespecified string of characters “guard”.

If a combination of particular pieces of structured-character-positioninformation satisfying the conditions described above is found, thepiece of structured-character-position information with the smallestcharacter-position value is selected from the particular pieces ofstructured-character-position information constituting each combination,and cataloged in the set of bit positions as a representative of thecombination.

FIG. 23 is a diagram showing the structure of the search-result datagenerated as a result of individual pieces of search processing. Asshown in this figure, the search-result data is organized intosub-groups, each of which comprises pieces ofstructured-character-position information included in the set of bitpositions. Pieces of structured-character-position informationpertaining to a sub-group have the same text identifier. The structureof the search-result data also includes a list with the sub-groups eachserving as a member of the list, and information indicating the totalnumber of detected texts. After being associated with a search-resultidentifier for uniquely identifying the search-result data, thesearch-result data is stored in the search-result-data storing area 1704as a member of a set of pieces of search-result data.

The following is a more detailed description of the processing carriedout at Step 1809 of the procedure shown in FIG. 18, in which a searchresult is transferred to a client making a search-result inquiringrequest in accordance with the contents of the request, with referenceto FIG. 24. FIG. 24 is a PAD showing details of the procedure fortransferring search-result data carried out at Step 1809.

Here, a search-result inquiring request itself comprises three portions:a specification of a search-result identifier, a specification of thetype of inquiry, and a specification of a text identifier. Depending onthe type of inquiry, the search-result inquiring request may not includea specification of a text identifier.

As shown in FIG. 24, the processing carried out at Step 1809 begins withStep 2401, at which the search-result data storing area 1704 is searchedfor search-result data indicated by a search-result identifier includedin the search-result inquiring request.

The flow then goes on to Step 2402 to determine the type of inquiry. Ifthe inquiry is about the number of detected texts, the flow proceeds toStep 2403. If the inquiry is about a text identifier, on the other hand,the flow proceeds to Step 2404. If the inquiry is aboutcharacter-position information, the flow proceeds to Step 2405.

At Step 2403, the number of detected texts is extracted from thesearch-result data retrieved from the search-result data storing area1704 at Step 2401, and transmitted to the client making the request,ending the process.

At Step 2404, a set of all text identifiers included in thesearch-result data retrieved from the search-result data storing area1704 at Step 2401 is gathered, and transmitted to the client making therequest, ending the process.

At Step 2405, a list of pieces of structured-character-positioninformation corresponding to the text identifier specified in theinquiry are extracted from the search-result data retrieved from thesearch-result data storing area 1704 at Step 240, and transmitted to theclient making the request, ending the process.

At this point, the explanation of the text searching server 102 providedby the present embodiment is completed.

The following is a description of a text searching client 103 or 104employed in the first embodiment of the present invention, withreference to FIGS. 1 and 25.

As shown in FIG. 25, the text searching client comprises a display unit201, a keyboard 202, a central processing unit (CPU) 203, acommunication control apparatus 206, a main memory unit 207, amagnetic-disk drive 208, and a system bus 209.

The display unit 201 is used for displaying a screen on which the userinteractively enters a search condition, and for displaying informationsuch as a search result. The keyboard 202 is used for entering a searchcondition and a command for requesting an operation, such as theactivation of search processing. The central processing unit 203executes a variety of programs constituting the functions of the textsearching client. The communication control unit 206 is used forcommunicating with the text searching server 102 through the network 105in order to exchange requests and data with the text searching server102.

The main memory unit 207 is used for storing a variety of programs to beexecuted for carrying out various kinds of processing by the textsearching client, and for holding data temporarily. The magnetic-diskdrive 208 is used for storing a text obtained as a search result andother data. The system bus 209 is used for connecting the display unit201, the keyboard 102, the central processing unit 203, thecommunication control apparatus 206, the main memory unit 207, and themagnetic-disk drive 208 with each other.

Including a work area 216, the main-memory unit 207 is used for storinga search-condition inputting program 2501, a search-result displayingprogram 2502, a client control program 2503, and a system program 215.The magnetic-disk drive 208 includes an already-analyzed-text-datastoring area 217 and a search-result-data storing area 1704.

The search-result inputting program 2501 inputs and interprets a searchcondition entered by the user in an interactive manner. Thesearch-result displaying program 2502 displays a search result receivedfrom the text searching server 102. The client control program 2503controls the activation and execution of the search result inputtingprogram 2501 and the search-result displaying program 2502, andexchanges requests and data with the text searching server 102 throughthe network 105. The system program 215 provides basic functions forexecuting the programs implementing the functions of the text searchingserver 102 on the computer, including inputting and outputting data fromand to peripheral devices. The work area 216 is used for storing datarequired temporarily in the execution of the programs.

As described above, in the present embodiment, requests and data areexchanged with the text searching server 102 by way of the network 105.Note, however, that it is also possible to build a configuration whereinanother portable medium, such as a floppy disk 205, an optical magneticdisk, or a writable optical disk, is used in place of the network 105.As an alternative, it is also possible to build a configuration whereinone or more text searching clients and the text searching server 102 areimplemented by a single computer so that no data transfers are neededbetween the text searching clients and the text searching server 102. Asanother alternative, it is also possible to build a configurationwherein the text searching client is connected to a printer for printinga search result.

FIG. 26 is a PAD showing an operational processing procedure of the textsearching client provided by the first embodiment of the presentinvention. As shown in this figure, the procedure begins with Step 2601,at which, activated by a client activating command entered via thekeyboard 202, the client control program 2503 receives the command formaking a request for a text search from the user and gets in aprocessing loop. The loop is continued until a request to halt theclient processing is entered via the keyboard 202.

In the loop of the step 2601, pieces of processing of Steps 2602 to 2605are repeated.

At Step 2602, the search-condition inputting program 2501 is executed toinput a search condition entered by the user in an interactive manner.The search condition is then converted into a request for a text searchthat can be readily interpreted by the text searching server 102. Then,the flow goes on to Step 2603, at which the request for a text search istransmitted to the text searching server 102 by way of the network 105.Subsequently, the flow proceeds to Step 2604 to wait for a search-resultidentifier to be transmitted by the text searching server 102 as aresponse to the request for a text search, and receives thesearch-result identifier as soon as it arrives.

The flow of the processing procedure then continues to Step 2605, atwhich the search-result displaying program 2502 is executed to input thesearch-result identifier. The search-result displaying program 2502displays a screen of the search-result data in response to an inquiryabout the search result made by the user in an interactive manner.

FIG. 27 is a PAD showing a detailed procedure carried out by thesearch-result inputting program 2501 at Step 2602. As shown in FIG. 27,the procedure begins with Step 2701, at which, invoked by the clientcontrol program 2503, the search-condition inputting program 2501displays a screen by which the user enters a search condition in aninteractive manner on the display unit 201.

The flow then goes on to Step 2702, at which a search conditionspecified by the user on the screen is read in.

Then, the flow proceeds to Step 2703, at which the search condition readin at Step 2702 is converted into a request for a text search that canbe readily interpreted by the text searching server 102.

FIG. 28 is a PAD showing a detailed procedure carried out by thesearch-result displaying program 2502 at Step 2605. As shown in thisfigure, the procedure begins with Step 2801, at which, activated by theclient control program 2503, the search-result displaying program 2502inputs a search-result identifier, immediately getting in a processingloop. The loop is continued until a request is entered by the user tohalt the processing to display a search result. In the loop of Step2801, pieces of processing of Steps 2802 to 2815 are repeated.

The loop of Step 2801 begins with Step 2802, at which a screen fordisplaying a search result and for the user to enter a request isdisplayed on the display unit 201. The flow then goes on to Step 2803,at which the contents of a request made by the user on the displayscreen are read in.

Then, the flow proceeds to Step 2804, at which the search-resultdisplaying program 2502 determines the type of request made by the user,making a decision as to which destination the flow is to branch independence on the type of request. More particularly, if the request isfor displaying the number of detected texts, the flow goes on to piecesof processing of Steps 2805 and 2806. If the request is for displaying alist of text identifiers for a group of detected texts, on the otherhand, the flow goes on to pieces of processing of Steps 2807 and 2808.If the request is for displaying the contents of a text, the flow goeson to pieces of processing of Steps 2809 to 2815. After all the piecesof processing at Step 2806, 2808, or 2815 (the last step of one of thebranch destinations) have been carried out, the flow returns to Step2802, resuming the loop.

At Step 2805, a detected-text-count inquiring request for making aninquiry about the number of detected texts is issued and transmitted tothe text searching server 102. The flow then goes on to Step 2806, atwhich the number of detected texts transmitted by the text searchingserver 102 in response to the detected-text-count inquiring request isreceived and displayed on the display unit 201.

At Step 2807, a text-identifier inquiring request for making an inquiryabout a list of text identifiers for a group of detected texts is issuedand transmitted to the text searching server 102. The flow then goes onto Step 2808, at which a set of text identifiers transmitted by the textsearching server 102 in response to the text-identifier inquiringrequest is received and a group of text identifiers included in the setare displayed on the display unit 201. At Step 2809, a text identifieridentifying a text to be displayed is input. The flow then goes on toStep 2810, at which a text-transfer request for obtainingalready-analyzed-text data of a text identified by the text identifieris issued and transmitted to the text searching server 102. The flowthen goes on to Step 2811, at which already-analyzed-text datatransmitted by the text searching server 102 in response to thetext-transfer request is received and stored in thealready-analyzed-text-data storing area 217.

Then, the flow proceeds to Step 2812, at which acharacter-position-information inquiring request for making an inquiryabout a position in the already-analyzed-text data at which a specifiedstring of characters included in a search condition was detected, isissued and transmitted to the text searching server 102. The flow thengoes on to Step 2813, at which a list of pieces ofstructured-character-position information transmitted by the textsearching server 102 in response to the character-position-informationinquiring request is received and stored in the search-result-datastoring area 1704.

Subsequently, the flow continues to Step 2814, at which a data treatingprocess for invertedly displaying a detected portion of a specifiedstring of characters at a text search time is carried out by referringto the already-analyzed-text data received at Step 2811 and the list ofpieces of structured-character-position information received at the step2813. The flow then proceeds to Step 2815, at which thealready-analyzed-text data which underwent the inversion processing atStep 2814 is formatted and displayed on the display unit 201.

At this point, the explanation of the operational procedure of the textsearching clients 103 and 104 provided by the first embodiment of thepresent invention is completed.

Second Embodiment

A second embodiment of the present invention is described as follows.

FIG. 29 is a diagram showing the configuration of a text catalogingsub-system 101 as implemented by the present embodiment.

The hardware configuration of the text cataloging sub-system 101 shownin FIG. 29 is identical to that implemented by the first embodimentshown in FIG. 2. In the case of the text cataloging sub-system 101provided by the second embodiment shown in FIG. 29, however, the mainmemory unit 207 stores a reversed-order-structure-index creating program2901 in addition to the programs stored in the main memory unit 207 ofthe first embodiment. The magnetic-disk drive 208 also has areversed-order-structure-index storing area 2902 in addition to theareas stored in the magnetic-disk drive 208 of the first embodiment. Thereversed-order-structure-index creating program 2901 catalogsinformation on the logical structure of already-analyzed-text data of atext to be cataloged into a reversed-order-structure index stored in thereversed-order-structure-index storing area 2902, updating thereversed-order-structure index.

In the present embodiment, the text-cataloging control program 214controls the activation and the execution of the text-structureanalyzing program 210, the structure-index creating program 211, thereversed-order-structure-index creating program 2901, thestructured-full-text-data generating program 212, and thecharacter-string-index creating program 213. The text-cataloging controlprogram 214 also transmits the already-analyzed-text data generated bythe text-structure analyzing program 210, the structure index generatedby the structure-index creating program 211, thereversed-order-structure index generated by thereversed-order-structure-index creating program 2901, and thecharacter-string index generated by the character-string-index creatingprogram 213 to the text searching server 102 by way of the network 105.

As described above, the present embodiment has a configuration wherein atext to be cataloged is input from the floppy disk 205. However, anotherkind of portable medium, such as an optical magnetic disk or a writableoptical disk, may be used in place of the floppy disk 205, withappropriate changes to the hardware and software. As an alternativeconfiguration, a text to be cataloged can also be input through thenetwork 105. In addition, in the configuration of the presentembodiment, the already-analyzed-text data generated by thetext-structure analyzing program 210, the structure index generated bythe structure-index creating program 211, the reversed-order-structureindex generated by the reversed-order-structure-index creating program2901, and the character-string index generated by thecharacter-string-index creating program 213 are transmitted to the textsearching server 102 by way of the network 105.

Furthermore, instead of using the network 105, a portable medium such asa floppy disk, an optical magnetic disk, or a writable optical disk canbe used for transferring the information. As an alternative, the textcataloging sub-system 101 and the text searching server 102 can beimplemented by a single computer so that no data transfers are neededbetween the text cataloging sub-system 101 and the text searching server102.

FIG. 30 is a PAD showing a procedure for cataloging a text according tothe second embodiment of the present invention. The procedure shown inthis figure is similar to that of the first embodiment shown in FIG. 3.However, FIG. 30 is different from FIG. 3 in that Step 3001 is insertedright after Step 305, and Step 308 is replaced by Step 3002.

At the newly inserted Step 3001, the reversed-order-structure-indexcreating program 2901 is executed, inputting the already-analyzed-textdata generated at Step 304. The reversed-order-structure-index creatingprogram 2901 retrieves the current reversed-order-structure index fromthe reversed-order-structure-index storing area 2902, catalogingstructure information of the input already-analyzed-text data in thecurrent reversed-order-structure index. Thereversed-order-structure-index creating program 2901 then stores backthe updated reversed-order-structure index in thereversed-order-structure-index storing area 2902.

At the new Step 3002, on the other hand, th e text-cataloging controlprogram 214 transmits all pieces of already-analyzed-text data stored inthe already-analyzed-text-data storing area 217, the structure indexstored in the structure-index storing area 218, thereversed-order-structure index stored in thereversed-order-structure-index storing area 2902, as well as thecharacter-string index stored in the character-string-index storing area220 to the text searching server 102 by way of the network 105.

FIG. 31 is a PAD showing details of the processing carried out at Step3001 of the procedure shown in FIG. 30, which is carried out by thereversed-order-structure-index creating program 2901.

As shown in FIG. 31, the processing procedure begins with Step 3101, atwhich the updated reversed-order-structure-index creating program 2901forms a judgment as to whether a reversed-order-structure index alreadyexists in the reversed-order-structure-index storing area 2902. If noreversed-order-structure index exists in thereversed-order-structure-index storing area 2902 yet, the flow goes onto Step 3102, at which the reversed-order-structure-index creatingprogram 2901 creates an initial-state (or empty)reversed-order-structure index. If a reversed-order-structure indexalready exists in the reversed-order-structure-index storing area 2902,on the other hand, the flow proceeds to Step 3103, at which thereversed-order-structure-index creating program 2901 retrieves thereversed-order-structure index from the reversed-order-structure-indexstoring area 2902.

The flow then continues to Step 3104, at which thereversed-order-structure-index creating program 2901 retrieves thealready-analyzed-text data of the text to be cataloged from thealready-analyzed-text-data storing area 217.

Then, the flow goes on to Step 3105, at which thereversed-order-structure-index creating program 2901 searches thealready-analyzed-text data for all nodes, that is, elements and piecesof character-string data, which form the tree-likereversed-order-structure of the already-analyzed-text data. Pieces ofprocessing of Steps 3106 to 3109 are repeated, with the nodes eachtreated as an object of processing.

At Step 3106, the reversed-order-structure-index creating program 2901forms a judgment on a node of the already-analyzed-text data currentlybeing processed (that is, a judgment as to whether a metanode associatedwith (or mutually corresponding to) the node exists in thereversed-order-structure index). A metanode is either a metaelement or apiece of meta-character-string data. If an associated metanode does notexist in the reversed-order-structure index, the flow goes on to Step3107, at which a metanode is created and cataloged in thereversed-order-structure index. The flow then proceeds to Step 3108, atwhich a reversed-order context identifier is assigned to the catalogedmetanode. A reversed-order context identifier is a number used foruniquely identifying a metanode in the reversed-order-structure index.

Then, the flow continues to Step 3109, at which thereversed-order-structure-index creating program 2901 adds an associativerelation between a node in the already-analyzed-text data currentlybeing processed and the reversed-order context identifier uniquelyidentifying the cataloged metanode in the reversed-order-structure indexassociated with the node to the already-analyzed-text data, updating thealready-analyzed-text data.

After Steps 3106 to 3109 have been repeated for all nodes, the flowcontinues to Step 3110, at which the updated already-analyzed-text datais output and stored in the already-analyzed-text-data storing area 217.Then, the flow goes on to Step 3111, at which the updatedreversed-order-structure index is output and stored in thereversed-order-structure-index storing area 2902, and thereversed-order-structure-index creating program 2901 ends theprocessing.

As described above, the procedure carried out by thereversed-order-structure-index creating program 2901 is similar to theprocedure carried out by the structure-index creating program 211 shownin FIG. 9. In the repetition of the pieces of processing of Steps 3106to 3109, however, the order of tracing the tree-like structure of thealready-analyzed text is different from that of the structure-indexcreating program 211, resulting in a reversed-order-structure indexhaving a tree-like structure different from the tree-like structure ofthe structure index produced by the structure-index creating program211.

When repeatedly carrying out the pieces of processing at Steps 3106 to3109 by treating each node composing the tree-like structure of thealready-analyzed-text data as an object, the individual nodes of thetree-like structure are processed by tracing the tree-like structure inan order to be explained by referring to FIG. 32. In this figure, anellipse represents an element node, whereas a rectangle represents acharacter-string node. If a node has a plurality of lower-level nodesdirectly subordinate to it, the lower-level nodes are represented byarranging them from the left to the right in the order in which theyappear in the already-analyzed-text data. A number, shown inside a nodeis a processing order number for the node.

As shown in this figure, the order in which a group of nodes areprocessed at Steps 3106 to 3109 starts with a node located at the rootof the tree-like structure. In addition, the order of processing of aspecific node and a group of lower-level nodes directly subordinate tothe specific node starts with the specific node, followed by processingof the lower-level nodes in an order opposite to the order in which theyappear in the tree-like structure, beginning with the right-mostdirectly subordinate node.

With reference to FIG. 33, the following is a detailed description ofthe processing carried out at Step 3106 on a node of thealready-analyzed-text data currently being processed to form a judgmentas to whether a metanode associated with the node exists in thereversed-order-structure index. FIG. 33 is a diagram showing anassociative relation between a group of nodes composing the tree-likestructure of the already-analyzed-text data shown on the left-hand sideof the figure, and a group of nodes (metanodes) composing the tree-likestructure of the reversed-order-structure index for thealready-analyzed-text data shown on the right-hand side of the figure.

Here, in the present embodiment, a node in already-analyzed-text dataand a metanode in a reversed-order-structure index created for thealready-analyzed-text data are defined to be associated with each other(or to mutually correspond to each other) if thereversed-order-tree-like-structure address of the node in the tree-likestructure of the already-analyzed-text data is the same as thereversed-order-tree-like-structure address of the metanode in thetree-like structure of the reversed-order-structure index created forthe already-analyzed-text data. A reversed-order-tree-like-structureaddress of a specific node in a tree-like structure ofalready-analyzed-text data is a sequence of code pairs which aredetermined when tracing a path in the tree-like structure starting fromthe root of the tree-like structure and ending at the specific node inan order of descending node level.

Each pair of codes represents a node encountered in the traced path. Thefirst code in each couple indicates the type of the node. Particularly,the first code indicates whether the node is an element or a piece ofcharacter-string data and, if the node is an element, the first codealso indicates the type of element. The second code in each couple is anumber indicating a position in an order of appearance of the node amongbrother nodes (nodes pertaining to the same type in the tree-likestructure), with the last node among the brother nodes regarded as thefirst one in the order of appearance. The pairs of codes are arranged inthe chronological order in which the respective nodes are encounteredalong the traced path. A reversed-order-tree-like-structure address of ametanode in the tree-like structure of a reversed-order structure indexis defined in the same way as a node. In order to distinguish areversed-order-tree-like-structure address from an ordinarytree-like-structure address, each number in the former has the negativesign as a prefix thereof.

Taking a group of nodes composing the already-analyzed-text data shownon the left-hand side of FIG. 33 as an example, and finding thetree-like-structure addresses of some nodes in the tree-like structure,a node 3301 in the group is the root node in the tree-like structurewhich does not have a node directly superordinate thereto. Thetree-like-structure address of a node 3304 is found by tracing thetree-like structure of the already-analyzed-text data shown, startingfrom the root node 1101.

Since the node 3301 is found to be a first one among brother nodespertaining to an element node “thesis”, thereversed-order-tree-like-structure address of the node 3301 is“/thesis[−1]”. Tracing the tree-like structure further, a node 3302 isfound to be a node directly subordinate to the node 3301 and the lastone among brother nodes pertaining to the an element node “chapter ”.Thus, the reversed-order-tree-like-structure address of the node 3302 is“/thesis[−1]/chapter[−1]”. By the same token, thereversed-order-tree-like-structure address of a node 3303 can bedescribed as “/thesis[−1]/chapter[−1]/paragraph[−2]”. This is becausethe node 3303 is directly subordinate to the node 3302 and a second onefrom the last among brother nodes pertaining to the an element node“paragraph”. Likewise, the reversed-order-tree-like-structure address ofa node 3304 can be described as“/thesis[−1]/chapter[−1]/paragraph[−2]/comment[−1]”. This is because thenode 3304 is directly subordinate to the node 3303 and the last oneamong brother nodes pertaining to the an element node “comment”.

Reversed-order-tree-like-structure addresses of metanodes composing thetree-like structure of the reversed-order-structure index shown on theright-hand side of FIG. 33 are found in the same way as nodes of thealready-analyzed-text data on the left-hand side of the figure. Thereversed-order-tree-like-structure address of a metanode 3305 is“/thesis[−1]”, which is the same as that of the node 3301. Similarly,the reversed-order-tree-like-structure address of a metanode 3306 is“/thesis[−1]/chapter[−1]”, which is the same as that of the node 3302,and the reversed-order-tree-like-structure address of a metanode 3307 is“/thesis[−1]/chapter[−1]/paragraph[−2]”, which is the same as that ofthe node 3303. Thus, the metanodes 3305, 3306, and 3307 are judged to beassociated with the nodes 3301, 3302, and 3303 respectively at Step 3106of the processing procedure shown in FIG. 31.

Since the reversed-order-structure index shown in FIG. 33 does notinclude a metanode that has the same reversed-order-tree-like-structureaddress as the node 3304 of the already-analyzed-text data, the node3304 is judged not to have a metanode associated with it in thereversed-order-structure index. Thus, a new metanode associated with thenode 3304 is created and cataloged in the reversed-order-structure indexat Step 3107.

A new metanode associated with a node is cataloged in thereversed-order-structure index at Step 3107 by adding the new metanodeto the head of a group of metanodes directly subordinate to ahigher-level metanode associated with a higher-level node directlysuperordinate to the node, and assigning a type corresponding to thetype of the node to the new metanode. Thus, in the case of the node3304, a new metanode associated with the node 3304 is cataloged in thereversed-order-structure index at Step 3107 by adding the new metanodeto the head of a group of metanodes directly subordinate to thehigher-level metanode 3307 associated with the higher-level node 3303directly superordinate to the node 3304, and assigning the type“comment” corresponding to the type of the node 3304 to the newmetanode.

The following is a description of a process to develop areversed-order-structure index by sequentially superposing a pluralityof pieces of already-analyzed-text data one after another, withreference to FIG. 34. In this figure, reference numerals 3401, 3403, and3405 each denote a piece of already-analyzed-text data of a text to becataloged. The tree-like structures of the pieces ofalready-analyzed-text data are sequentially superposed on areversed-order-structure index in a process of developing thereversed-order-structure index.

When the already-analyzed-text data 3401 of Text 1 is input at aninitial stage, the reversed-order-structure index is in an initial (orempty) state. In this case, a tree-like structure equivalent to that ofthe already-analyzed-text data 3401 is cataloged in thereversed-order-structure index, resulting in thereversed-order-structure index state denoted by reference numeral 3402.At that time, context identifiers −E1, −E2, −E3, −E4, and −E5 areassigned to metaelements newly created in the reversed-order-structureindex 3402, whereas context identifiers −C1, −C2, and −C3 are assignedto newly created pieces of meta-character-string data.

Next, when the already-analyzed-text data 3403 of Text 2 is input, nodesin the tree-like structure of the already-analyzed-text data 3403overlapping those of the existing reversed-order-structure index 3402are not processed. In other words, only nodes in the tree-like structureof the already-analyzed-text data 3403 with no corresponding ones in theexisting reversed-order-structure index 3402 (that is, only hatchednodes in the tree-like structure of the already-analyzed-text data 3403)are newly cataloged in the reversed-order-structure index 3402. At thattime, context identifiers −E6 and −E7 are assigned to metaelements newlycataloged in the reversed-order-structure index 3402, whereas a contextidentifier −C4 is assigned to a newly cataloged piece ofmeta-character-string data, resulting in the reversed-order-structureindex state denoted by reference numeral 3404.

Then, when the already-analyzed-text data 3405 of Text 3 is input, nodesin the tree-like structure of the already-analyzed-text data 3405overlapping those of the existing reversed-order-structure index 3404are not processed. In other words, only nodes in the tree-like structureof the already-analyzed-text data 3405 with no corresponding ones in theexisting reversed-order-structure index 3404 (that is, only hatchednodes in the tree-like structure of the already-analyzed-text data 3405)are newly cataloged in the reversed-order-structure index 3404. At thattime, context identifiers −E8, −E9, and −E10 are assigned tometaelements newly cataloged in the reversed-order-structure index 3404,whereas context identifiers −C5 and −C6 are assigned to newly catalogedpieces of meta-character-string data. When the cataloging of the threepieces of already-analyzed-text data 3401, 3403, and 3405 has beencompleted, the reversed-order-structure index takes the state denoted byreference numeral 3406.

FIG. 35 is a PAD showing details of the processing carried out at Step306 of the procedure shown in FIG. 30, which is carried out by thestructured-full-text-data generating program 212 of the presentembodiment. As shown in FIG. 35, the procedure carried out by thereversed-order-structured-full-text-data generating program 212 of thepresent embodiment is similar to that of the first embodiment shown inFIG. 13. However, the present embodiment is different from the firstembodiment in that Step 3501 is introduced as a substitute for Step1305.

At Step 3501, a context identifier and a reversed-order contextidentifier for a character-string-data node currently being processedare found from the already-analyzed-text data and output to thestructured-full-text-data storing area 219.

FIG. 36 is a diagram showing the format in which structured-full-textdata is output to a file by the structured-full-text-data generatingprogram 212. FIG. 36 exemplifies a case in which structured-full-textdata is generated from the SGML text shown in FIG. 5. As shown in FIG.36, the format of a file for storing structured-full-text data adoptedin the present embodiment starts with a text identifier, followedrepetitively by as many sets of three pieces of information as there arepieces of character-string data in the text. The three pieces ofinformation are a context identifier, a reversed-order contextidentifier, and a descriptive complete string of characters associatedwith the context identifiers.

A character-string index of the present embodiment is created accordingto the same procedure as that of the first embodiment shown in FIG. 15.FIG. 37 is a diagram showing the data structure of a character-stringindex used in the present embodiment. In more detail, FIG. 37 is adiagram showing a portion of the data structure of a character-stringindex obtained at a stage where an operation to catalog a group ofpartial character strings included in the structured-full-text datashown in FIG. 36 into the character-string index has been completed atthe end of processing of the structured-full-text data carried out bythe character-string-index creating program 213. The portion of the datastructure of the character-string index corresponds to the descriptivecomplete string of characters, “an example of transformation”.

As shown in FIG. 37, the character-string index of the presentembodiment is also used for holding reversed-order context identifiers,in addition to the pieces of information kept in the character-stringindex of the first embodiment shown in FIG. 16. Much like thecharacter-string index of the first embodiment, the character node forthe last character “n” of the descriptive complete string of charactersand the structured-character-position information for the last characterare omitted from the portion of the data structure of thecharacter-string index shown in FIG. 16. In addition, the position ofthe head character of a partial string of characters in the descriptivecomplete string of characters is expressed as a position relative to X,the position of a character immediately preceding the descriptivecomplete character string.

At this point, the explanation of the text cataloging sub-system 101provided by the present embodiment is completed.

Next, the text searching server implemented by the second embodiment ofthe present invention, that is, the apparatus denoted by referencenumeral 102 in FIG. 1, is explained.

FIG. 38 is a diagram showing the configuration of the text searchingserver 102 implemented by the present embodiment. As shown in thisfigure, the text searching server 102 has areversed-order-structure-index storing area 2902 in the magnetic-diskdrive 208, in addition to the configuration elements of the textsearching server 102 provided by the first embodiment.

Also in the present embodiment, requests and data are exchanged betweenthe text cataloging sub-system 101 and the text searching clients 103and 104 by way of the network 105. However, it is also possible toemploy a portable medium, such as the floppy disk 205, an opticalmagnetic disk, or a writable optical disk in place of the network 105.As an alternative, the text cataloging sub-system 101 and the textsearching server 102 may be implemented by a single computer so that nodata transfers are needed between the text cataloging sub-system 101 andthe text searching server 102. As another alternative, one or more textsearching clients and the text searching server 102 may be implementedby a single computer so that no data transfers are needed between thetext searching clients and the text searching server 102.

FIG. 39 is a PAD showing a procedure for searching a text adopted by thesecond embodiment of the present invention. As shown in this figure, theprocedure for searching a text adopted by the second embodiment issimilar to that of the first embodiment shown in FIG. 18. However, theprocedure for searching a text adopted by the second embodiment isdifferent from that of the first embodiment in that Step 3901 is carriedout in place of Step 1805. At Step 3901, an updated character-stringindex, an updated reversed-order-structure index, and an updatedstructure index reflecting the contents of a group of newly catalogedtexts are received from the text cataloging sub-system 101 and stored inthe character-string-index storing area 220, thereversed-order-structure-index storing area 2902, and thestructure-index storing area 218, respectively.

FIG. 40 is a PAD showing details of the processing carried out at Step1806 of the processing shown in FIG. 39, which is a carried out by thesearch-condition analyzing program 1701 of the present embodiment.

The procedure shown in FIG. 40 begins with Step 4001, at which thesearch-condition analyzing program 1701 is invoked by a request for atext search, including a specified search condition as an input to theprogram, forming a judgment on a structure condition included in thesearch condition. If the search condition includes a normal-orderstructure condition, that is, the same structure condition as the firstembodiment, pieces of processing of Steps 1902 and 1903 are carried out.Here, the pieces of processing of Steps 1902 and 1903 are the same asthose of the first embodiment. If the search condition includes areversed-order structure condition, on the other hand, pieces ofprocessing of Steps 4002 and 4003 are carried out. If the searchcondition does not include a reversed-order structure condition or anormal-order structure condition, however, the flow goes on to Step1904.

At Step 4002, the reversed-order-structure index is retrieved from thereversed-order-structure-index storing area 2902. The flow then proceedsto Step 4003, at which the reversed-order-structure index is searchedfor a set of reversed-order context identifiers of all pieces ofcharacter-string data included in the reversed-order-structure indexwhich satisfies the structure condition. The set of reversed-ordercontext identifiers is referred to hereafter as areversed-order-context-identifier set.

The pieces of processing carried out at Steps 1904, 1905, and 1906 arethe same as those of the first embodiment. After the processing carriedout at Step 1903, 4003, or 1906 is completed, the flow goes on to a step4004.

At Step 4004, the search-condition analyzing program 1701 generatesalready-developed-search-condition data comprising the set of contextidentifiers found at Step 4003, the specified string of charactersincluded in the search condition, and the list of partial characterstrings generated at Step 1905 or 1906, terminating the processing.

FIG. 41 is a diagram showing an example of generation of thealready-developed-search-condition data in processing carried out by thesearch-condition analyzing program 1701 in the present embodiment.

In this figure, reference numeral 4101 denotes an example of a searchcondition specified in a request for a text search. As shown in thisfigure, the search condition 4101 comprises a specification of areversed-order-structure condition “chapter/comment[−1]” and aspecification of a character-string condition “guard”. The searchcondition 4101 specifies a search of the reversed-order-structure indexto be carried out for a case in which a string of characters “guard”appears in a last element “comment” directly subordinate to an element“chapter”.

Assuming that the contents of the reversed-order structure index are asshown by reference numeral 4102, since the structure condition specifiedin the search condition is a reversed-order structure conditionprescribing a search to be started from the end of the structure, as aresult of the search of the reversed-order-structure index carried outat Step 4003 of the processing procedure shown in FIG. 40, “comment”elements satisfying the specification of the reversed-order-structurecondition are found out to be those having context identifiers −E3 and−E12. Thus, pieces of character-string data directly subordinate tothese “comment” elements (that is, pieces of character-string data withthe context identifiers −C1 and −C7) must be next searched for a case inwhich the string of characters “guard” appears. In the character-stringindex to be used in the search, however, only appearance positions ofpartial character strings each having a length of two characters arecataloged. Thus, a direct search for a specified string of three or morecharacters like the string “guard” cannot be carried out.

In order to solve this problem, the search-condition analyzing program1701 sequentially extracts a group of partial character strings, each ofwhich has a character count of two from the specified string ofcharacters, starting with the partial string of characters at the headof the specified string of characters, while shifting the extractedposition by one character at a time until the last partial string ofcharacters of the specified string of characters is extracted. Theprogram then generates a list of partial character strings, includingthe extracted partial character strings, as members thereof at Step1905. In the case of the specified string of characters “guard”, thelist of partial character strings extracted from the specified stringhas the partial character strings “gu”, “ua”, “ar”, and “rd” as itsmembers.

As a result, already-analyzed-search-condition data 4103, whichcomprises an empty context-identifier set, a reversed-ordercontext-identifier set (−C1, −C7), the specified string of characters“guard”, and a list of partial character strings (“gu”, “ua”, “ar”, and“rd”) as shown in FIG. 41, is generated at Step 4004 of the procedureshown in FIG. 40.

FIG. 42 is a PAD showing details of the processing carried out at Step1807 of the procedure shown in FIG. 39, which is carried out by thecharacter-string-index searching program 1702 of the present embodiment.

The character-string-index searching program 1702 is activated,inputting already-developed-search-condition data generated by thesearch-condition analyzing program 1701. As shown in FIG. 42, theprocedure carried out by the character-string-index searching program1702 of the present embodiment is similar to that of the firstembodiment. However, the procedure carried out by thecharacter-string-index searching program 1702 of the present embodimentis different from that of the first embodiment in that, in the case ofthe present embodiment, pieces of processing of Steps 4201, 4202, and4203 are carried out in place of those of the Steps 2104, 2105, and2107, respectively, of the first embodiment shown in FIG. 21.

At Step 4201, the character-string index is searched for partialcharacter strings matching the specified string of characters, and a setof pieces of structured-character-position information corresponding tothe partial character strings are found. Then, only a group of pieces ofstructured-character-position information, each of which has a contextidentifier included in the set of context identifiers of thealready-developed-search-condition data or a reversed-order contextidentifier included in the set of reversed-order context identifiers ofthe already-developed-search-condition data, are extracted from the setof pieces of structured-character-position information. Finally, a setof bit positions composed of the extracted group of pieces ofstructured-character-position information is created.

Much like Step 4201, at Step 4202, the character-string index is firstsearched for partial character strings matching the specified string ofcharacters, and a set of pieces of structured-character-positioninformation corresponding to the partial character strings are found. Inthis case, however, since the character count of the specified string ofcharacters is smaller than the length of a partial string of characters,the character-string index is searched for partial character strings,the front portion of each of which matches the specified string ofcharacters. The front portion of a partial string of characters is theportion starting with the head character and ending with a characternode corresponding to the end character of the specified string ofcharacters. Then, only a group of pieces ofstructured-character-position information, each of which has a contextidentifier included in the set of context identifiers of thealready-developed-search-condition data or a reversed-order contextidentifier included in the set of reversed-order context identifiers ofthe already-developed-search-condition data, are extracted from thegroup of pieces of structured-character-position information. Finally, aset of bit positions composed of the extracted group of pieces ofstructured-character-position information is created.

At Step 2106, processing of Step 4203 is repeated for each of thepartial character strings that constitute the list of partial characterstrings in the already-developed-search-condition data. At Step 4203,the character-string index is searched for a partial string ofcharacters, and a set of pieces of structured-character-positioninformation corresponding to the partial string of characters is found.Then, only a group of pieces of structured-character-positioninformation, each of which has a context identifier included in the setof context identifiers of the already-developed-search-condition data ora reversed-order context identifier included in the set ofreversed-order context identifiers of thealready-developed-search-condition data, are extracted from the set ofpieces of structured-character-position information. Finally, theextracted group of pieces of structured-character-position informationare stored by being associated with the partial string of characters.

The processing carried out at Step 2108 of the procedure shown in FIG.42 (that is, the concatenation judging process carried out by thecharacter-string-index searching program 1702) is the same as that ofthe first embodiment shown in FIG. 22. In the case of the secondembodiment, however, if the search condition specifies a reversed-orderstructure condition, a concatenation judgment is formed by finding outwhether the reversed-order context identifiers of the partial characterstrings to be concatenated match each other, instead of finding outwhether the context identifiers of the partial character strings to beconcatenated match each other.

As described above, according to the configuration provided by thepresent embodiment, it is possible to carry out a search operationspecifying a structure condition of tracing the logical structure of atext in the reversed order (that is, tracing the logical structure of atext starting from the end of the text) in addition to a variety ofstructure conditions that can be used in a search operation in the firstembodiment. Examples of a structure condition of tracing the logicalstructure of a text in the reversed order are “Search the last chapterof a thesis for a specific string of characters” and “Search a secondreference from the end of a list of references for a specific string ofcharacters”.

At this point, the explanation of the second embodiment of the presentinvention is completed.

Third Embodiment

Next, a third embodiment provided by the present invention is described.

The configuration of the structured-text cataloging/searching systemimplemented by the present embodiment and the procedures of the programsthereof are the same as those of the first embodiment, except that theway a node in the tree-like structure of already-analyzed-text data isassociated with a metanode in the structure index in the presentembodiment is different from that in the first embodiment. As a result,even if the same group of texts are input, the third embodiment willresult in a structure index with a data structure and assignment ofcontext identifiers that are different from those of the firstembodiment.

An associative relation between a group of nodes constituting thetree-like structure of already-analyzed-text data and a group of nodes(strictly speaking, metanodes) constituting the tree-like structure of astructure index created for the already-analyzed-text data in thepresent embodiment is explained by referring to FIG. 43. FIG. 43 is adiagram showing an associative relation between a group of nodescomposing the tree-like structure of already-analyzed-text data shown onthe left-hand side of the figure and a group of metanodes composing thetree-like structure of a structure index for the already-analyzed-textdata shown on the right-hand side of the figure.

Also in the case of the present embodiment, a node inalready-analyzed-text data and a metanode in a structure index createdfor the already-analyzed-text data are defined to be associated witheach other if the tree-like-structure address of the node in thetree-like structure of the already-analyzed-text data is the same as thetree-like-structure address of the metanode in the tree-like structureof the structure index, as is the case with the first and secondembodiments. However, the third embodiment is different from the firstand second ones in that, in the case of the third embodiment, withrespect to the order of appearance among brother nodes of the same typehaving a common direct superordinate node, the second node isdistinguished from the head node but the second and subsequent nodes arenot distinguished from each other. The number in a tree-like-structureaddress representing a position in the order of appearance is either [1]to indicate a head node or [2] to indicate a second or subsequent nodesin the order of appearance among brother nodes. The number in atree-like structure address representing a position in the order ofappearance never has a value of [3] or greater.

Considering a group of nodes composing the already-analyzed-text datashown on the left-hand side of FIG. 43 as an example, thetree-like-structure address of a node 4304 is found in the group. Asshown in this figure, a node 4301 in the group is the root node in thetree-like structure which does not have a node directly superordinatethereto. The tree-like-structure address of a node 4304 is found bytracing the tree-like structure of the already-analyzed-text data shown,starting from the root node 4301.

Since the node 4301 is a first one among brother nodes pertaining to theelement node “thesis”, the tree-like-structure address of the node 4301is “/thesis[1]”. Tracing further the tree-like structure, a node 4302 isfound to be directly subordinate to the node 4301. The node 4302 is afirst one among brother nodes pertaining to the element node “chapter”.Thus, the tree-like-structure address of the node 4302 is“/thesis[1]/chapter[1]”. By the same token, the tree-like-structureaddress of a node 4303 can be described as“/thesis[1]/chapter[1]/paragraph[2]”, because the node 4303 is directlysubordinate to the node 4302 and a fourth one among brother nodespertaining to the element node “paragraph”.

In spite of the fact that the node 4303 is a fourth one among brothernodes pertaining to the an element node “paragraph”, it is notdistinguished from the second one and, hence, identified by a code“/paragraph[2]” instead of “/paragraph[4]”. Likewise, thetree-like-structure address of a node 4304 can be described as“/thesis[1]/chapter[1]/paragraph[2]/comment[2]”, because the node 4304is directly subordinate to the node 4303 and a second one among brothernodes pertaining to the element node “comment”.

Tree-like-structure addresses of metanodes that constitute the tree-likestructure of the structure index shown on the right-hand side of FIG. 43are found in the same way as the nodes of the already-analyzed-text dataon the left-hand side of the figure. The tree-like-structure address ofa metanode 4305 is “/thesis[1]”, which is the same as that of the node4301. Similarly, the tree-like-structure address of a metanode 4306 is“/thesis[1]/chapter[1]”, which is the same as that of the node 4302, andthe tree-like-structure address of a metanode 4307 is“/thesis[1]/chapter[1]/paragraph[2]”, which is the same as that of thenode 4303. Thus, the metanodes 4305, 4306, and 4307 are judged to beassociated with (or mutually correspond to) the nodes 4301, 4302, and4303, respectively. It should be noted that, since the structure indexshown in FIG. 43 does not include a metanode that has the sametree-like-structure address as the node 4304 of thealready-analyzed-text data, the node 4304 is judged not to have ametanode associated with it in the structure index.

As a result of the addressing rule described above, there will never beadded three or more metanodes of the same type to a structure indexcreated in the third embodiment, or there will be no more than twometanodes of the same type in the three-like structure of a structureindex, because the third and subsequent nodes of the same type in thetree-like structure of already-analyzed-text data have the same contextidentifier as the second one assigned thereto. For this reason, with thetext searching method provided by the present embodiment, it is nolonger possible to specify any arbitrary appearance order in a structurecondition. To be more specific, it is possible to distinguish only afirst element from the second or subsequent ones among elements of thesame type. When the structure condition is restricted as describedabove, the data structure of the structure index of the presentembodiment becomes simple in comparison with that of the first andsecond embodiments, allowing the size of the structure-index storingarea 218 to be reduced.

In spite of the fact that the associative relation between nodes andmetanodes described above is embraced in the present embodiment, astructure condition of tracing an order of appearance starting from theend of the order can be specified if two structure indexes (that is, thenormal-order and reversed-order structure indexes) are provided inadvance, as is the case with the second embodiment.

At this point, the explanation of the third embodiment is completed.

Fourth Embodiment

A fourth embodiment applying the present invention is described next.

FIG. 44 is a diagram showing the configuration of a text catalogingsub-system 101 as implemented by the present embodiment.

The text cataloging sub-system 101 shown in FIG. 44 is similar to thatimplemented by the first embodiment shown in FIG. 2 as far as thehardware configuration and the configuration of the magnetic disk 208are concerned. In the case of the text cataloging sub-system 101provided by the fourth embodiment shown in FIG. 44, however, the mainmemory unit 207 also stores a text-structure normalizing program 4401,in addition to the programs stored in the main memory unit 207 of thefirst embodiment.

In the present embodiment, the text-cataloging control program 214controls the activation and the execution of the text-structureanalyzing program 210, the text-structure normalizing program 4401, thestructure-index creating program 211, the structured-all-text-datagenerating program 212, and the character-string-index creating program213. The text-cataloging control program 214 also transmits thealready-analyzed-text data generated by the text-structure analyzingprogram 210, the structure index generated by the structure-indexcreating program 211, and the character-string index generated by thecharacter-string-index creating program 213 to the text searching server102 by way of the network 105.

As described above, the present embodiment has a configuration wherein atext to be cataloged is input from the floppy disk 205. However, it isalso possible to use another kind of portable medium, such as an opticalmagnetic disk or a writable optical disk, in place of the floppy disk205. As an alternative configuration, a text to be cataloged can also beinput through the network 105.

In addition, in the configuration of the present embodiment, thealready-analyzed-text data generated by the text-structure analyzingprogram 210, the structure index generated by the structure-indexcreating program 211, and the character-string index generated by thecharacter-string-index creating program 213 are transmitted to the textsearching server 102 by way of the network 105. Instead of using thenetwork 105, though, the present invention can also use a portablemedium such as a floppy disk, an optical magnetic disk, or a writableoptical disk for transferring the information. As an alternative, it isalso possible to implement the text cataloging sub-system 101 and thetext searching server 102 by a single computer so that no data transfersare needed between the text cataloging sub-system 101 and the textsearching server 102.

FIG. 45 is a PAD showing a procedure for cataloging a text adopted bythe fourth embodiment of the present invention. The procedure shown inthis figure is similar to that of the first embodiment shown in FIG. 3.However, the present procedure is different from that of FIG. 3 in thatStep 4501 is inserted right after Step 304.

At the newly inserted Step 4501, the text-structure normalizing program4401 is executed to input already-analyzed-text data generated at Step304. The text-structure normalizing program 4401 extracts a structureand a descriptive complete string of characters which are, as an objectto be searched, improper from the already-analyzed-text data and deletesthem.

FIG. 46 is a PAD showing the procedure carried out by the text-structurenormalizing program 4401. As shown in this figure, the procedure beginswith Step 4601, at which the text-structure normalizing program 4401finds out whether normalization parameters are specified upon theinvocation of the text-structure normalizing program 4401. If thenormalization parameters are specified, the flow goes on to pieces ofprocessing at Steps 4602 to 4608. If the normalization parameters arenot specified, on the other hand, the processing is completed withoutdoing anything.

The normalization parameters are parameters for specifying the types ofa connection element and a deletion element. A connection element is anon-structural element used, for example, for putting emphasis on thedisplay of a portion of a text. During a search operation, it isnecessary to search the text for a string of characters by passing overthe boundaries of a non-structural element. On the other hand, adeletion element holds data therein with a type different from that ofthe native contents of the text, so that, in a search operation, thetext should be searched for a string of characters by ignoring thecontents of the deletion element. An example of a deletion element is anelement for embedding a link to a reference to be referred to in a text.

At Step 4602, the specified normalization parameters are read in. Here,the normalization parameters can be specified by inputs entered via thekeyboard 202, by storing them in a file in advance, or by using anothermeans. The types of a plurality of connection elements and deletionelements can be specified or omitted. The flow then goes on to Step4603, at which already-analyzed-text data is retrieved from thealready-analyzed-text-data area 217.

Then, the flow proceeds to Step 4604, at which the tree-like structureof the already-analyzed-text data is sequentially traced for elementnodes, one node after another, and pieces of processing at Steps 4605 to4607 are carried out repeatedly for all element nodes. After the piecesof processing have been completed for all the nodes, the flow continuesto Step 4608.

At Step 4605, the text-structure normalizing program 4401 determines thetype of element that the normalization parameter specifies for anelement node currently being processed. If the type of element indicatesthat the element being processed is specified as a connection element,the flow goes on to Step 4606, at which the node of the element isdeleted and all character strings in the connection element areconcatenated with character strings before and after the connectionelement. If the type of element indicates that the element beingprocessed is specified as a deletion element, on the other hand, theflow goes on to Step 4607, at which the node of the element and alllower-level nodes directly subordinate to the node of the element aredeleted.

After the processing at Step 4605 and the subsequent Step 4606 or 4607has been completed, the flow continues to Step 4608, at which a group ofelements to be normalized are processed, and the updatedalready-analyzed-text data is stored back in thealready-analyzed-text-data storing area 217.

FIG. 47 is a diagram showing an example of the normalization processing.

In this figure, reference numeral 4701 denotes normalization parameters.In this example, the types of two connection elements are specified as“bold” and “italic” whereas the names of two deletion elements arespecified as “link” and “index”. In this case, if a portion having astructure like that denoted by reference numeral 4702 exists inalready-analyzed-text data, connection processing is carried out at Step4606 for the type “bold”. A result of the connection processing isdenoted by reference numeral 4703. If a portion having a structure likethat denoted by reference numeral 4704 exists in already-analyzed-textdata, on the other hand, deletion processing is carried out at Step 4607for the type “link”. A result of the deletion processing is denoted byreference numeral 4705.

As described above, after normalization processing has been carried outfor already-analyzed-text data, cataloging the normalizedalready-analyzed-text data in a structure index, and subsequent piecesof processing are performed in the present embodiment so that the textcan be searched without encountering a hindrance by non-structuralelements included in the text prior to the cataloging.

In spite of the fact that normalization processing is embraced in thepresent embodiment, a structure condition of tracing an order ofappearance from the end of the order can yet be specified if twostructure indexes (that is, a normal-order and reversed-order structureindexes) are prepared in advance, as is the case with the secondembodiment.

At this point, the explanation of the fourth embodiment of the presentinvention is completed.

According to the methods of searching a structured text provided by thepresent invention as described above, since a condition regarding anappearance position of a logical element in a text can be included in aspecification of a structure condition, it is possible to carry out asearch operation specifying a structure condition in detail on a textdatabase comprising a large number of texts, each of which has acomplicated logical structure.

Various modifications of the embodiments set forth in the foregoingdescription will become apparent to those of ordinary skill in the art.All such modifications that basically rely on the teachings throughwhich the invention has advanced the state of the art are properlyconsidered within the spirit and scope of the invention.

We claim:
 1. In a structured-text cataloging method for a text searching system in which a set of texts is searched for specific text contents, a character-string-index updating step comprising the sub-steps of: extracting partial character strings each having a predetermined character count, character-position information of said partial character strings in a text to be cataloged, a text identifier for uniquely identifying said text in a text database, and a context identifier of a metanode representing character-string data including said partial character strings in a structure index, from said character-string data included in said text for each of a plurality of texts to be cataloged; generating structured-character-position information that includes said character-position information, said text identifier, and said context identifier; and updating a character-string index by cataloging an associative relation between each of said partial character strings and said structured-character-position information in said character-string index.
 2. A structured-text cataloging method for a text searching system, in which a set of texts is searched for specific text contents, comprising the following steps: a structure-index creating step of creating a structure index, by sequentially superposing logical structures of a plurality of texts to be cataloged in said structure index; wherein said structure index has a tree-like structure composed of a plurality of metanodes; wherein a context identifier that uniquely identifies one of said metanodes is assigned to each metanode of said structure index; wherein a group of structure elements having the same position of appearance and the same element type for a plurality of texts are represented by a single metanode; and wherein the tree-like structures of two of said texts to be cataloged are superposed on each other in said structure index by: comparing nodes of one of said tree-like structures of said two texts with nodes of the other of said tree-like structures of said two texts; regarding a root node in said one of said tree-like structures as a counterpart that mutually corresponds to a root node in said other of said tree-like structures; regarding a non-root node in said one of said tree-like structures of said two texts as a counterpart that mutually corresponds to a non-root node in said other of said tree-like structures if the non-root node in said one of said tree-like structures has a directly superordinate node mutually corresponding to a directly superordinate node of the non-root node in said other of said tree-like structures, if the non-root node in said one of said tree-like structures is the same type of node as the non-root node in said other of said tree-like structures, and if either both the non-root node in said one of said tree-like structures and the non-root node of said other of said tree-like structures are head nodes of an array of brother nodes of the same type of node, or both the non-root node in said one of said tree-like structures and the non-root node of said other of said tree-like structures are not head nodes of an array of brother nodes of the same type of node; and representing two nodes mutually corresponding nodes by a single metanode in said structure index.
 3. A structured-text cataloging method for a text searching system, in which a set of texts is searched for specific text contents, comprising the following steps: a structure-index creating step of creating a structure index, by sequentially superposing logical structures of a plurality of texts to be cataloged in said structure index; wherein said structure index has a tree-like structure composed of a plurality of metanodes; wherein a context identifier that uniquely identifies one of said metanodes is assigned to each metanode of said structure index; wherein a group of structure elements having the same position of appearance and the same element type for a plurality of texts are represented by a single metanode; and wherein the tree-like structures of two of said texts to be cataloged are superposed on each other in said structure index by: comparing nodes of one of said tree-like structures of said two texts with nodes of the other of said tree-like structures of said two texts; regarding a root node in said one of said tree-like structures as a counterpart that mutually corresponds to a root node in said other of said tree-like structures; regarding a non-root node in said one of said tree-like structures of said two texts as a counterpart that mutually corresponds to a non-root node in said other of said tree-like structures if the non-root node in said one of said tree-like structures has a directly superordinate node mutually corresponding to a directly superordinate node of the non-root node in said other of said tree-like structures, if the non-root node in said one of said tree-like structures is the same type of node as the non-root node in said other of said tree-like structures, and if either both the non-root node of said one of said tree-like structures and the non-root node of said other of said tree-like structures are end nodes of an array of brother nodes of the same type of node, or both the non-root node of said one of said tree-like structures and the non-root node of said other of said tree-like structures are not end nodes of an array of brother nodes of the same type of node; and representing two nodes corresponding to each other by a single metanode in said structure index.
 4. A structured-text cataloging method for a text searching system, in which a set of texts is searched for specific text contents, comprising the following steps: obtaining already-analyzed-text data from an analysis of a logical structure of a text to be cataloged in a text database; searching said already-analyzed-text data for a structure and a descriptive complete string of characters which are regarded as improper objects to be searched; deleting the structure and the descriptive complete string of characters from the already-analyzed-text data for an improper object found in said searching step; and cataloging said already-analyzed-text data in said text database.
 5. A computer-readable storage medium storing a structure index created by executing said character-string-index updating step of said structured-text cataloging method according to claim
 1. 6. A computer-readable storage medium encoded with executable instructions constituting a program which, when executed by a computer, causes the computer to implement said character-string-index updating step of said structured-text cataloging method according to claim
 1. 7. A structured-text cataloging method for a text searching system, in which a set of texts is searched for specific text contents, comprising the following steps: a structure-condition judging step of searching a structure index for a set of context identifiers satisfying a specified structure condition; a structured-character-position-information extracting step of extracting partial character strings from a search term, each extracted partial character string having a predetermined character count, and searching a character-string index for a set of pieces of structured-character-position information matching said extracted partial character strings; and an index searching step of searching said set of pieces of structured-character-position information for specific pieces of structured-character-position information that have context identifiers included in said set of context identifiers found at said structure-condition judging step, and that have a positional relation among said specific pieces of structured-character-position information matching an order of arrangement of said partial character strings in said search term.
 8. A computer-readable storage medium encoded with executable instructions constituting a program which, when executed by a computer, causes the computer to implement said structure-condition judging step, said structured-character-position-information extracting step, and said index searching step of said structured-text searching method according to claim
 7. 